Tech Eval: Introduce `Environment` kind/CRD to synchronize GitLab Environments with GitLab Agent

Topic to Evaluate

Evaluating Environment kind/CRD described in #352186 (closed). The goal is to make sure that users can create, update and destroy GitLab Environments through GitLab Agent with Custom Resource Definition (a.k.a CRD).

For the feature direction, please watch this video.

Tasks prior to evaluation

• Clearly document the topic to evaluated in this issue description
• Determine specific scope including time-bounds for investigation

Tasks to Evaluate

• How can users create CRD in their cluster? What would the UX look like?
• How can users create custom objects (which is kind: Environment)? This would be just adding a resource file in their repository.
• How can we monitor the custom objects in KAS? We need to get familiar with the business logic of KAS.
• How can we send API request to GitLab from KAS? e.g. Do we use public API and if so how do we authenticate/authorize?

After Evaluatation

• Determine feasibility of the feature
• Create issue for implementation or update existing implementation issue description with implementation proposal
• Set weight on implementation issue
• If weight is greater than 5, break issue into smaller issues

Risks and Implementation Considerations

Team

• Add workflowplanning breakdown typefeature and the corresponding ~devops::<stage> and ~group::<group> labels.
• Ping the PM and EM.