[RFE] Enable/Disable automate domains

ManageIQ recently implemented the create_from_git action on /api/automate_domains. By default the new domain is set to disabled. This is by design, because there should be an administrator "approving" the domain, by enabling it manually.

However CI/CD pipelines need to enable the new domains automatically.
My particular use case involves generating Automate Domains on the fly, based on pull requests in git. These Domains are pushed to the central git repo as orphaned branch, a call to create_from_git that imports the domain, before the orphaned branch is cleaned up.

A separate action to set the enabled field in MiqAeDomain would solve that problem

Original RFE: https://github.com/ManageIQ/manageiq-api/issues/354
PR: https://github.com/ManageIQ/manageiq-api/pull/571
My Project: https://github.com/ThomasBuchinger/miq-flow/issues/52
Gitter conversation:

• https://gitter.im/ManageIQ/api?at=5d509e5f4e17537f5215b319
• https://gitter.im/ManageIQ/api?at=5d52b8b39507182477cedd2b

Start at the /api/automate_domains entry point and review the existing create_from_git action, then inspect how the enabled field is represented on MiqAeDomain. Use the referenced PR 571 and related discussion to understand the intended enable/disable behavior. Done means the API supports the requested domain state change for CI/CD use.