EE: 45560 provide zero configuration domain name for auto devops using nip io

See CE counterpart MR

What does this MR do?

• Implements EE multi-cluster ingress default domains
  • Implements EE override for DeploymentPlatform#find_cluster
  • Moves AUTO_DEVOPS_DOMAIN to project#auto_devops_domain_variable, which is then used in CI::Build#persisted_environment_variables

This follows the following rules of precedence :

1. cluster(s) IP based domain
2. Auto DevOps domain or instance domain
3. CI scoped variables (Settings > CI/CD > Variables, AUTO_DEVOPS_DOMAIN, with any environment scope)

NOTE : The move to deployment_variables basically means that AUTO_DEVOPS_DOMAIN variable will now only be available for the jobs that sets a environment in the gitlab-ci.yaml file.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Add support for multi-cluster scenario

Screenshots (if relevant)

Development tasks

• Support multiple ingress default domains
  • add deployment_cluster to DeploymentPlatform
  • Move user provided value for AUTO_DEVOPS_DOMAIN from project#predefined_variables to project#deployment_variables
  • Set ingress default_domain for each environment in project#predefined_variables
• [-] Help text for multiple clusters

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• [-] API support added
• Tests added for this feature/bug
• Conforms to the code review guidelines
  • Has been reviewed by a UX Designer
  • [-] Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • [-] Has been reviewed by a Database specialist
• EE specific content should be in the top level /ee folder
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• [-] Conforms to the database guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• [-] If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/45560