Draft: POC to capture executor from runner

What does this MR do and why?

This POC aims to propose a rough idea of a solution for #345361 (closed) and #14335 (closed).

Result:

Runners get updated with their executor in the UI, users can search by executor now 🚀

This POC:

• Captures the runner executor information when a runner requests new jobs
• Stores the executor as a tag, in lieu of database modifications

The final product should:

• Capture the runner executor in other (more relevant) steps of the runner lifecycle
• Validate the executor sent is one of the valid options (?)
• Store the executor in a separate database column

Screenshots or screen recordings

Result: Executor is auto-updated in the UI

How to set up and validate locally

Warning! Your runners tags data may be changed running this POC!

1. Start the gitlab-runner with some live runners
2. Wait for runners to ask for jobs (should be a few seconds)
3. Check the runner admin UI for http://gdk.test:3000/admin/runners
4. Tags are enhanced with executors.

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.

Related to #345361 (closed)