This PR changes to use relative database paths by default. The default mode is to store all databases in the same folder.
With this update, the paths stored in the server database can now be relative, in which case they are resolved relative to the datafolder.
This makes it simpler to move the data folder as the paths are not stored in full.
For new backups, relative paths are assigned.
For existing backups, the full paths are retained.
If the database path is updated manually, the path will be made relative, if it is relative to the datafolder; otherwise a full path is stored.
This fixes#6677
Kenneth Skovhede
5c1b477cda