fix: table location mappings to /etc/s3tables (#8457)

* fix: move table location mappings to /etc/s3tables to avoid bucket name validation

Fixes #8362 - table location mappings were stored under /buckets/.table-location-mappings
which fails bucket name validation because it starts with a dot. Moving them to
/etc/s3tables resolves the migration error for upgrades.

Changes:
- Table location mappings now stored under /etc/s3tables
- Ensure parent /etc directory exists before creating /etc/s3tables
- Normal writes go to new location only (no legacy compatibility)
- Removed bucket name validation exception for old location

* refactor: simplify lookupTableLocationMapping by removing redundant mappingPath parameter

The mappingPath function parameter was redundant as the path can be derived
from mappingDir and bucket using path.Join. This simplifies the code and
reduces the risk of path mismatches between parameters.

weed/s3api/s3tables/utils.go

@@ -21,7 +21,7 @@ const (
 )
 
 const (
-	tableLocationMappingsDirName = ".table-location-mappings"
+	tableLocationMappingsDirPath = "/etc/s3tables"
 	tableObjectRootDirName       = ".objects"
 )
 
@@ -111,7 +111,7 @@ func GetTableObjectBucketPath(bucketName string) string {
 
 // GetTableLocationMappingDir returns the root path for table location bucket mappings
 func GetTableLocationMappingDir() string {
-	return path.Join(TablesPath, tableLocationMappingsDirName)
+	return tableLocationMappingsDirPath
 }
 
 // GetTableLocationMappingPath returns the filer path for a table location bucket mapping