Allow sync Godot addons with local repos for auto updating

[azur-wolve]

As of now addon creators can notify within the Godot Editor when an addon has a new version (presumably from GitHub), per-project.

But if have a personal addon stored locally on one's machine there's no direct way to update the godot projects that use it when the addon gets updated, so must be done manually.

Having a way to notify and auto-update would prevent cases where forget to manually update the addon for specific projects.
(Unless there's a way that I'm not aware of)

[Calinou]

• Related to Ability to put plugins in gitignore and download them after cloning #2263,
  Install an add-on manifest to allow downloading add-ons when opening a project #7925,
  Implement support for updating plugins inside the editor #8451
  and Add support for installing/managing addons via Git URL #8780.