Feature: Modified usernames

### Is there an existing request for this feature?

- [X] I have searched the existing issues and found none that matched mine

### Describe the feature

When logging in using an Entra email ID (e.g., `bill@foo.com`), the username and home directory on the VM are the full email address (e.g., `/home/bill@foo.com`).

For orgs with only one login domain, it would be great to have the username not include the `@foo.com` portion. So the username in this case would be `bill` and the home directory would be `/home/bill`.

### Describe the ideal solution

_No response_

### Alternatives and current workarounds

_No response_

### System information and logs

_No response_

### Relevant information

_No response_

### Double check your logs

- [X] I have redacted any sensitive information from the logs