[research/poc] Use share-manager for managing space memberships

[rhafer]

• howto rework the space listing, especially with regards to personal spaces
• try to avoid different mechanisms per space type
• what about existing setups (migrations?)
• possible options for caching

Acceptance Criteria:

• ADR

related to: #2183

[rhafer]

• howto rework the space listing, especially with regards to personal spaces

The current way to list spaces (e.g. /me/drives) via the CS3 ListStorageSpaces() call can probably stay as it is. That is probably not going away anytime soon. We could however also utilize GetSharedWithMe() in the future, which might have
some (performance benefits)

• try to avoid different mechanisms per space type

Ideally Personal Spaces would also (upon creation) add an entry to the share manager

• what about existing setups (migrations?)

Existing space grants needs to be imported into the share manager once. Would be extra nice if this could happen without interruptive to the running cloud.

• possible options for caching

Not sure what was meant with this, but AFAIK the (jsoncs3) share-manager already implements caching. However we need to add more filtering options e.g. to be able to efficiently to query like:

• give me only spaces
• give me everything that is not a space

[rhafer]

Just for completeness: The gateway already has a config switch for using the shareprovider for spaces: https://github.com/opencloud-eu/reva/blob/main/internal/grpc/services/gateway/usershareprovider.go#L43 (I guess the eos backend used that)

[rhafer]

Also: With this change we'd might be able to get rid of that hacky permission ids on the graph api for space permissions (https://github.com/opencloud-eu/opencloud/blob/main/services/graph/pkg/service/v0/base.go#L582).

We could just use the shareid like for "normal" shares instead of that u:<userid> or g:<groupid> hack.

[rhafer]

Also²: The share-manager is able to track who added a member to the space and when. This info is not available on the space grants in the storage provider.

Update: This is not quite true the grant attribute at least have the creator id as a property.

[rhafer]

I just created #2492 to illustrate the required changes.