feat: Add support for custom Auth0 domains

[bendiknesbo]

Description

This PR adds support for a new environment-variable&prompt for setting an audience that is not based off of the auth0 domain. This allows auth0-checkmate to be run with a custom domain instead of the canonical auth0-domain, since the canonical auth0-domain may be blocked via network ACLs. The Auth0 Management API audience is controlled by Auth0, and thus will always be in the format https://<tenant-name>.<region-identifier>.auth0.com/api/v2/ (where region-identifier is optional), but the custom-domains can be anything, like login.travel0.com

References

• GitHub Issue: Allow connecting to custom domains with clientID&secret #134
• Auth0 Network ACL: https://auth0.com/docs/secure/tenant-access-control-list
• Example Network ACL that blocks canonical auth0 domain: https://auth0.com/docs/secure/tenant-access-control-list/use-cases#enforce-traffic-through-specific-infrastructure

Testing

I have not added tests for the reading of the environment-variables or the prompts during CLI-run, as there are no tests for those files at all today.

• This change adds test coverage for new/changed/fixed functionality

Checklist

• I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not the default branch

This PR was pair-programmed by me and @etameem