feat(cloud-registry): show the registry's field errors #536

Problem

The service create form shows only a general error when Cloud Registry rejects a registration with 400, so users don't see which field is wrong.

Proposal

Use the field-error support of @elixir-cloud/design (#535) in the Cloud Registry components (create form; edit forms where they exist): map the registry's field errors (elixir-cloud-aai/cloud-registry#317) to the form's fields, show them there, and keep the general error for responses without field errors. No validation rules in the component; the registry has the final say. Update the component docs and the event documentation.

Supersedes #453. Blocked by #535 and elixir-cloud-aai/cloud-registry#317.