New ticket field for "Requested GitLab.com Username" to GitLab.com Zendesk form

Please add a new ticket field to the GitLab.com ticket form titled Requested GitLab.com Username.

This field should display when the selected Problem Type is Request inactive username and should be required.

Draft description to show to end users:

Enter the username only, without the preceding URL (e.g., "User" instead of "gitlab.com/User")

This will contribute to work in #1496 (moved).

/cc @gitlab-com/support/managers for approval