fix: error when freeipa transforms external trusted user name when adding them to a group

[infra-monkey]

Fixes #21

When adding a trusted to an external group, multiple formats are allowed DOMAIN\User, DOMAIN\group , username@domain and it is case insensitive.
However the added name is transformed to a lowercase upn format username@domain
When a transformation of the name happens during the add, the creation of the membership succeeds on freeipa but the read operation fails on the next step because there is a mismatch between the resource declaration and the response from freeipa.

With this fix, I check after creation that the name defined in the resource is defined as a member of the group responded by freeipa. If not, I delete the user membership in freeipa and exit without saving the resource in the state.
If the name is a member of the group, then, I continue as normal and save the resource in the state.

This is implemented only for external user group member ship.