Update examples and add tests for multiple identities

[ishuar]

This pull request includes updates to the examples and tests for creating multiple user-managed identities and assigning roles to them. It also includes a new example for creating multiple identities using a combination of Azure built-in and custom roles.

[github-actions]

Test Results ⚙️ Status: success

• Test Output:

multiple-identities.tftest.hcl... in progress
  run "multiple_identities"... pass
multiple-identities.tftest.hcl... tearing down
multiple-identities.tftest.hcl... pass

Success! 1 passed, 0 failed.

• Test Error Message:

Pusher: @ishuar, Action: pull_request, Workflow: Module Testing