Optionally return status on WriteRelationships

[benvernier-sc]

This PR is part of a proof of concept for authzed/spicedb#1903.

It adds a with_status boolean field on WriteRelationshipsRequest, and creates a new RelationshipUpdateStatus type that gets included in WriteRelationshipsResponse if with_status was true in the request.

There are 4 possible statuses:

• no_op: the input operation was a no-op (either a TOUCH on a relation that already existed as-is, or a DELETE on a relation that didn't exist, I didn't differentiate between them),
• created: the input operation led to a relationship being created (from either a CREATE or TOUCH),
• deleted: the input operation led to a relationship being deleted (from a DELETE),
• updated: the input operation led to a relationship being updated, and the status includes both the old and the new relationships (from a TOUCH where caveats differed from what was stored).

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