When a new unsynced space is discovered, add it to the synced folders

[TheOneRing]

Depends on #11750

[saw-jan]

Tested on ownCloud 6.0.0.14688-daily20240918 [967f29]

All available spaces (personal, shares, project-space) are sync when adding new account

[TheOneRing]

Tested on ownCloud 6.0.0.14688-daily20240918 [967f29]

All available spaces (personal, shares, project-space) are sync when adding new account

With the branding enabled, also new spaces added on the server side are automatically synced.