Feature Request: backup metadata read/write information instead of write only

[Drazzilb08]

This idea came about from using the backup function that was recently added to develop branch and noticing that it was overwriting my current metadata/entries (namely my tmdb_movies entires on my movies.yml file (now mind you this is using the movies.yml file as the backup location)).

As per our conversation here https://discord.com/channels/822460010649878528/917322922765463562/936630936588677150

The idea behind this is to have PMM do a lot of the heavy lifting/writing for it to make all the blank entries for movies/series/music (blank entries for collections would be nice too with the ability for it to be separate files).
After those blank entries have been written then you can go back in and edit those entries by adding tmdb_movie or other entires.

Furthermore with a sync option if you edit something within plex it will reflect on the movies.yml file and vice versa.

This would be great for those who add things frequently but don't won't to input all the entries every time something is added. PMM will do this automatically. All you have to do is go in and edit what metadata you want to change from either plex or PMM config and it's visible in both places.