feat: List users by metadata (#10415)

# Which Problems Are Solved

Some users have reported the need of retrieving users given a metadata
key, metadata value or both. This change introduces metadata search
filter on the `ListUsers()` endpoint to allow Zitadel users to search
for user records by metadata.

The changes affect only v2 APIs.

# How the Problems Are Solved

- Add new search filter to `ListUserRequest`: `MetaKey` and `MetaValue`
  - Add SQL indices on metadata key and metadata value
  - Update query to left join `user_metadata` table

# Additional Context

  - Closes #9053
  - Depends on https://github.com/zitadel/zitadel/pull/10567

---------

Co-authored-by: Silvan <27845747+adlerhurst@users.noreply.github.com>
Co-authored-by: Stefan Benz <46600784+stebenz@users.noreply.github.com>

(cherry picked from commit 8df402fb4f)

internal/query/projection/user_metadata.go

@@ -49,6 +49,8 @@ func (*userMetadataProjection) Init() *old_handler.Check {
 		},
 			handler.NewPrimaryKey(UserMetadataColumnInstanceID, UserMetadataColumnUserID, UserMetadataColumnKey),
 			handler.WithIndex(handler.NewIndex("resource_owner", []string{UserGrantResourceOwner})),
+			handler.WithIndex(handler.NewIndex("metadata_key", []string{UserMetadataColumnKey})),
+			handler.WithIndex(handler.NewIndex("metadata_value", []string{UserMetadataColumnValue})),
 		),
 	)
 }