Grant 3rd party invites and ensure that they aren't replayable

[cognivore]

Why?

• We let root invite to be completeable as often as the endpoint can be called
• It means that we should move it to Foreign pipeline when we are done with rate limiting!
• We also grant our users two invites so that they can invite their friends. These invites are delayed
• These two invites are represented by a single object in the DB, a credential with kind: invite
• It is necessary that when a user shares an invite object with Alice, Alice can't reshare object to Bob thus draining credential
• We think that this precaution is already implemented in fulfill_do, but we need to test it

How?

• Implement granting the delayed invites in invite controller
• Write a test that shows that when a new PK / DID gets registered, another can't be registered using the same invite object