updater: Retain legacy module path support

The updater itself is distributed and updated for all versions of OBS
for which updates are still available. As such, it needs to be aware
of the legacy plugin location for versions before v33 and the new
location for v33 onwards.

When checking if the browser plugin exists, check both locations.

When installing the virtual cam, we reference the manifest for the
version we are updating to and use the appropriate location.
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f