Allow `owners` and `members` to be email ids instead of just objectIDs

[asajoshi]

What problem are you facing?

I want to write a composition that allows creating a Group by accepting owners and members as email IDs. currently the provider only supports Object IDs for these parameters. So for this to work , I will have to create a separate function that can retrieve the Object ID from Email ID.

This might be an easier fix in the provider.

This is the example claim I want to make work with the provider

apiVersion: groups.example.com/v1alpha1
kind: ADGroup
metadata:
  name: examplegroup
spec:
  parameters:
    displayName: demogroup
    owners:
      - example.user@example.com
    members:
      - example.user2@example.com
      - example.user2@example.com

[asajoshi]

duplicates #125