Change data paths according to semantic.work conventions

[erikap]

Change paths of mounted folders to be more in line with other services:

• Persist the update handler's state in /data instead of /config
• Mount files in /share instead of /data

This is a breaking change. Tried to be backwards compatible but it's very hard since the user has to update the mount points in docker-compose.yml. An upgrade path is documented in the changelog.

[nvdk]

I guess this needs to be done, though in the past we opted to have the update-store in config specifically for backwards compatibility (and not having to change the file mount path).
I think this PR could be improved by some startup checks so we can warn users if they have not properly moved the update store or if we detect other files than the update-store in /data.