feat(project_mirror): add ForceSyncProjectMirror

Prakash Divyrequested to merge
prakashdivyy/client-go:feat/add-force-sync-mirror into main

Add ForceSyncProjectMirror method to ProjectMirrorService to support triggering a manual update for a project mirror.

This maps to the POST /projects/:id/remote_mirrors/:mirror_id/sync API endpoint.

Merge request reports