[Database] Main projects that contain multiple repositories should be on their own table

[Dioscorides]

Many of the repositories in the DMMapp are part of bigger projects.
An example is ARCA / IHRT for many French Libraries: https://arca.irht.cnrs.fr/search?search%5Binput%5D=Brest&search%5Btype%5D=manuscripts

We currently add these parent projects manually, sometimes we forget to add them at all.

We should create a separate table where we can add these projects so that we can link to them / add them to the metadata of a library / etc. and make sure that the entries are always homogeneous.