[Concordia] Improve rate limiting

[abizjak]

Task description

The issuers have basic rate limiting now that is not persisted across restarts of the issuer services.

See #84

To make this more robust we should add a persistent rate limit.

[mh-concordium]

With the current solution, after 5 credentials were issued, user can try to issue new ones and after selecting "ADD" in bw, user will see the alert in teh frontend while the credentials will appear in the wallet being in Pending state "forever".

Proper solution would be to check whether there are already 5 credentials issued for the user id (Telegram/Discord) and then if that would be true, throw an error in the frontend while bw would not open.