s3tables: Rename tableMetadataInternal.Schema to Metadata

The field name 'Schema' was confusing given it holds a *TableMetadata struct
and serializes as 'metadata' in JSON. Rename to 'Metadata' for clarity and
consistency with the JSON tag and intended meaning.

weed/s3api/s3tables/utils.go

@@ -106,7 +106,7 @@ type tableMetadataInternal struct {
 	OwnerAccountID   string         `json:"ownerAccountId"`
 	VersionToken     string         `json:"versionToken"`
 	MetadataLocation string         `json:"metadataLocation,omitempty"`
-	Schema           *TableMetadata `json:"metadata,omitempty"`
+	Metadata         *TableMetadata `json:"metadata,omitempty"`
 }
 
 // Utility functions