add OCC command to migrate user_oidc accounts for direct authentication

[c-cal]

Accounts created using this connector at the first connection reside in the user_oidc table, and when you want to go back to direct authentication (after having removed this app), users cannot be found.

[jvllmr]

I think this feature would heavily depend on the selected OIDC provider. Such as the Keycloak admin api. Which raises the question: How can user_oidc acquire an access token which can be used to fetch all the users?