Feature request: list all registries for agent

[lenkan]

Currently, it is only possible to list registries for a particular AID. For some use cases it would be convenient to be able to list all registries for a particular agent.

Current behaviour:

GET /identifiers/{aid}/registries
=> Return all registries in agent that is owned by 'aid'

GET /identifiers/{aid}/registries/{regname}
=> Return registry 'regname' that is owned by 'aid'

Requested behaviour:

GET /registries
=> Return all registries in agent regardless of which aid is the owner

GET /registries?pre={aid name or prefix}
=> Return all registries in agent that is owned by 'aid'

GET /registries/{regname or registry key}
=> Return registry 'regname' regardless of which aid is the owner

Rationale

We want to have an overview of the registries that are controlled by a particular agent/wallet. Currently, the only way to do this is to iterate through all AIDs in the agent, then list all registries for each AID.