feat: delete metadata on SetOrganizationMetadata api (#11790)

# Which Problems Are Solved

Currently, to delete an Organization metadata key, callers must use a
separate
[DeleteMetadata](https://zitadel.com/docs/reference/api/org/zitadel.org.v2.OrganizationService.DeleteOrganizationMetadata)
API. This increases the complexity on client-side for operations where
metadata need to be synchronized.

# How the Problems Are Solved

Introduce deletion behavior to
[SetOrganizationMetadata](https://zitadel.com/docs/reference/api/org/zitadel.org.v2.OrganizationService.SetOrganizationMetadata):

When a metadata entry is passed with an empty value ("" / empty bytes):

- If the key exists → delete the key
- If the key does not exist → no-op (idempotent, no error)

# Additional Changes

n/a

# Additional Context

Relates to #11776

---------

Co-authored-by: Gayathri Vijayan <[email protected]>
Co-authored-by: Gayathri Vijayan <[email protected]>

internal/command/user_metadata.go

@@ -76,6 +76,7 @@ func (c *Commands) BulkSetUserMetadata(ctx context.Context, userID, resourceOwne
 	if err != nil {
 		return nil, err
 	}
+
 	// no changes for the metadata
 	if len(events) == 0 {
 		return writeModelToObjectDetails(&setMetadata.WriteModel), nil