Allow orga-files/folders to be accessible in meetings

[Elblinator]

Desired behaviour:

• If a file/folder is public then this file/folder needs to be displayed in every meeting
• Files/folders need a new flag to show that they are public.

[ostcar]

The first step is to add this new flag in the meta repo.

For the autoupdate service, this means, that when this flag is set, the requested mediafile can be seen by everyone. I would like to implement, that even anonymous can see such files. They can anyway, if one meeting allows anonymous users. It would be unnecessary complicated to check for that.

I transfer this issue to the meta repo. Since there currently is nothing, the autoupdate could do.

[luisa-beerboom]

After discussions with @bastianjoel we've come to the conclusion that the mediafiles meeting or organization specific data should be migrated to their own connective collections, since otherwise the requirement on setting access groups per meeting will not be solvable in a satisfactory manner