Import Role by Name

[denniskniep]

Description of your changes

There is a feature request around how to import objects via <realm/name> instead of #126

There are already some workarounds in place:

1. Using terraform import property (only a few resources supports that!)
2. Using crossplane functions to import the built-in objects of keycloak (see here)

This is a proposal how to import resources by name. Code changes are only affecting role resource as an example and foundation for discussions.

We could use a custom implementation of ExternalName config (see here and here)

• GetIDFn: Use defined props to lookup the Id used in the specific keycloak instance for that resource (i.e. by realmId, clientId & roleId). This could be done by using the terraform projects´s keycloakClient (i.e. kcClient.GetRoleByName(ctx, realmId.(string), clientId.(string), name.(string)))
• GetExternalNameFn: Builds the ExternalName based on deterministic props (i.e. <realmId>/<clientId>/<roleId>)

What do you think about this approach?

Topics to clarify:

• External Name and some props are overlapping. In case of role resource realmId, clientId & roleId are specified in properties as well as in external name. As far as I know there is a concept to mitigate that: OmittedFields & SetIdentifierArgumentFn. Issue with that is, that we can´t specify ClientIDRef which is a big downside!

Fixes #126