DPS: implement AccessTokenDataStore

[paullatzelsperger]

Feature Request

In order to keep track of valid tokens, the data plane needs to have a record of AccessTokenData objects.
Those are POJOs that contain information about the claims and the DataAddress associated with a transfer:

public record AccessTokenData(ClaimToken claimToken, DataAddress address, String id)

For testing/demo purposes we should have an in-memory implementation, but for production scenarios we need a persistent
store based on Postgres.

Which Areas Would Be Affected?

data plane

Why Is the Feature Desired?

data plane instances need to be able to validate the access token on an incoming data request.