[ADR] Select a GitLab Runner Executor

[Racer159]

Is your feature request related to a problem? Please describe.

Currently our GitLab runner solution is written for kubernetes-based runners though these have limitations that prevent things like docker-based workloads and other lower level development from being ran and tested within the environment.

Describe the solution you'd like

We should investigate the different GitLab runner executors (https://docs.gitlab.com/runner/executors/) and select one (or multiple) that we will support to meet the following:

• Ability to provide (even limited) runners in different on-prem environments
• Able to provide runners for Docker-based-workloads (this can be cloud-only)
• Jobs should be ephemeral
• The solution doesn't have to run alongside / in the rest of UDS

Additional context

This should consider cloud as primary and on-prem as secondary for now - not all features need to be on-prem but cloud should have a solid and secure developer experience.