[keycloak-dev] Client ID and Client ClientID - I propose we remove one

We have both "id" and "client-id" for clients in Keycloak at the moment. This seems unnecessary and complex. The model can retrieve clients on either value. In token endpoints the "client-id" is used. In admin endpoints the "id" is used. Also, in most cases it would be simpler for users to just have a generated id than having to come up with one themselves. The id doesn't have to be human readable either as we have name for that. OpenID Connect expects "client-id" to be generated by the IdP and can't be changed once created. I propose we remove "client-id" and only keep id. For migration of existing clients we would set the "id" value to the current value of "client-id". This would require no changes to adapter configs. When creating new clients from the admin console we would not allow setting the "client-id", instead just display it after the client was created. When importing clients it would be possible to set the id (and for backwards compatibility we would set "id" equal to the "client-id" field.