WIP: Adds `Ci::BuildEnvironmentDeployment` relationship

What does this MR do?

Adds Ci::BuildEnvironmentDeployment relationship

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

Architectural review

Why was this MR needed?

On Protected Environments we're fetching an environment per build on certain conditions. This implies a performance issue as fetching environments is very expensive to evaluate. The relationship Ci::Build - Environment - Deployment aims to help with the performance

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Conforms to the code review guidelines
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• 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
• End-to-end tests pass (package-and-qa manual pipeline job)

To do

• Modify CreateDeploymentService to fill Ci::BuildEnvironmentDeployment#deployment_id
• EE Port

Issue

https://gitlab.com/gitlab-org/gitlab-ce/issues/49954