A0CLI-49: add initial custom-domains support

[rene00]

Description

This PR adds initial Custom Domains support to auth0-cli.

It also bumps briandowns/spinner to latest version to resolve a race condition issue (see briandowns/spinner#99). I was hitting this race condition with the unit tests that accompany this PR.

List all custom domains:

$ auth0 custom-domains list

Create a new custom domain:

$ auth0 custom-domains create --domain example.org --type auth0_managed_certs --verification-method txt

Get a custom domain:

$ auth0 custom-domains get --custom-domain-id myCustomDomainID

Verify a custom domain:

$ auth0 custom-domains verify --custom-domain-id myCustomDomainID

Delete a custom domain:

$ auth0 custom-domains delete --custom-domain-id myCustomDomainID

References

• https://auth0team.atlassian.net/browse/A0CLI-49
• https://auth0.slack.com/archives/C01KGNSRS4C/p1611709375340300

Testing

• 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 master

[cyx]

Thanks mate!