Set gitlab agent's context to run kubectl command

What does this MR do and why?

This MR sets the gitlab agent’s context to run kubectl commands after agent-based cluster integration has been added. The review-apps agent has been added to the project: https://gitlab.com/gitlab-org/gitlab/-/cluster_agents/review-apps

Related to #359229 (closed)

Testing

• An example review-deploy job: https://gitlab.com/gitlab-org/gitlab/-/jobs/3386110050
  • A gitlab agent's context was set at #L93.
• An example review-cleanup job: https://gitlab.com/gitlab-org/gitlab/-/jobs/3382457542
  • A gitlab agent's context was set at #L37.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.