Strip v query param from gitlab_project.avatar_url

Summary

Previously, when storing a project's avatar URL, the full URL (including any extra tracking or cache-busting parameters like ?v=...) was saved as-is. This could cause unnecessary differences to be detected between the stored state and the actual value, even when the avatar itself hadn't changed.

This change introduces a small helper function that cleans up the avatar URL by removing the v query parameter before saving it. Now, when a project's avatar URL is recorded, it is stored in a consistent, stripped-down format, reducing false positives when checking for changes.

Fixes #6890 (closed)