fix(s3): include static identities in listing operations (#8903)

* fix(s3): include static identities in listing operations

Static identities loaded from -s3.config file were only stored in the
S3 API server's in-memory state. Listing operations (s3.configure shell
command, aws iam list-users) queried the credential manager which only
returned dynamic identities from the backend store.

Register static identities with the credential manager after loading
so they are included in LoadConfiguration and ListUsers results, and
filtered out before SaveConfiguration to avoid persisting them to the
dynamic store.

Fixes https://github.com/seaweedfs/seaweedfs/discussions/8896

* fix: avoid mutating caller's config and defensive copies

- SaveConfiguration: use shallow struct copy instead of mutating the
  caller's config.Identities field
- SetStaticIdentities: skip nil entries to avoid panics
- GetStaticIdentities: defensively copy PolicyNames slice to avoid
  aliasing the original

* fix: filter nil static identities and sync on config reload

- SetStaticIdentities: filter nil entries from the stored slice (not
  just from staticNames) to prevent panics in LoadConfiguration/ListUsers
- Extract updateCredentialManagerStaticIdentities helper and call it
  from both startup and the grace.OnReload handler so the credential
  manager's static snapshot stays current after config file reloads

* fix: add mutex for static identity fields and fix ListUsers for store callers

- Add sync.RWMutex to protect staticIdentities/staticNames against
  concurrent reads during config reload
- Revert CredentialManager.ListUsers to return only store users, since
  internal callers (e.g. DeletePolicy) look up each user in the store
  and fail on non-existent static entries
- Merge static usernames in the filer gRPC ListUsers handler instead,
  via the new GetStaticUsernames method
- Fix CI: TestIAMPolicyManagement/managed_policy_crud_lifecycle was
  failing because DeletePolicy iterated static users that don't exist
  in the store

* fix: show static identities in admin UI and weed shell

The admin UI and weed shell s3.configure command query the filer's
credential manager via gRPC, which is a separate instance from the S3
server's credential manager. Static identities were only registered
on the S3 server's credential manager, so they never appeared in the
filer's responses.

- Add CredentialManager.LoadS3ConfigFile to parse a static S3 config
  file and register its identities
- Add FilerOptions.s3ConfigFile so the filer can load the same static
  config that the S3 server uses
- Wire s3ConfigFile through in weed mini and weed server modes
- Merge static usernames in filer gRPC ListUsers handler
- Add CredentialManager.GetStaticUsernames helper
- Add sync.RWMutex to protect concurrent access to static identity
  fields
- Avoid importing weed/filer from weed/credential (which pulled in
  filer store init() registrations and broke test isolation)
- Add docker/compose/s3_static_users_example.json

* fix(admin): make static users read-only in admin UI

Static users loaded from the -s3.config file should not be editable
or deletable through the admin UI since they are managed via the
config file.

- Add IsStatic field to ObjectStoreUser, set from credential manager
- Hide edit, delete, and access key buttons for static users in the
  users table template
- Show a "static" badge next to static user names
- Return 403 Forbidden from UpdateUser and DeleteUser API handlers
  when the target user is a static identity

* fix(admin): show details for static users

GetObjectStoreUserDetails called credentialManager.GetUser which only
queries the dynamic store. For static users this returned
ErrUserNotFound. Fall back to GetStaticIdentity when the store lookup
fails.

* fix(admin): load static S3 identities in admin server

The admin server has its own credential manager (gRPC store) which is
a separate instance from the S3 server's and filer's. It had no static
identity data, so IsStaticIdentity returned false (edit/delete buttons
shown) and GetStaticIdentity returned nil (details page failed).

Pass the -s3.config file path through to the admin server and call
LoadS3ConfigFile on its credential manager, matching the approach
used for the filer.

* fix: use protobuf is_static field instead of passing config file path

The previous approach passed -s3.config file path to every component
(filer, admin). This is wrong because the admin server should not need
to know about S3 config files.

Instead, add an is_static field to the Identity protobuf message.
The field is set when static identities are serialized (in
GetStaticIdentities and LoadS3ConfigFile). Any gRPC client that loads
configuration via GetConfiguration automatically sees which identities
are static, without needing the config file.

- Add is_static field (tag 8) to iam_pb.Identity proto message
- Set IsStatic=true in GetStaticIdentities and LoadS3ConfigFile
- Admin GetObjectStoreUsers reads identity.IsStatic from proto
- Admin IsStaticUser helper loads config via gRPC to check the flag
- Filer GetUser gRPC handler falls back to GetStaticIdentity
- Remove s3ConfigFile from AdminOptions and NewAdminServer signature

docker/compose/s3_static_users_example.json

@@ -0,0 +1,53 @@
+{
+  "identities": [
+    {
+      "name": "admin",
+      "credentials": [
+        {
+          "accessKey": "AKIAIOSFODNN7EXAMPLE",
+          "secretKey": "wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY"
+        }
+      ],
+      "actions": [
+        "Admin",
+        "Read",
+        "List",
+        "Tagging",
+        "Write"
+      ]
+    },
+    {
+      "name": "steward",
+      "credentials": [
+        {
+          "accessKey": "steward-key",
+          "secretKey": "steward-secret"
+        }
+      ],
+      "actions": [
+        "Read",
+        "List",
+        "Write"
+      ]
+    },
+    {
+      "name": "le001",
+      "credentials": [
+        {
+          "accessKey": "le001-key",
+          "secretKey": "le001-secret"
+        }
+      ],
+      "actions": [
+        "Read",
+        "List"
+      ]
+    },
+    {
+      "name": "anonymous",
+      "actions": [
+        "Read"
+      ]
+    }
+  ]
+}