CI Minutes Cost Factors: finish the Dev track

To close the Development Track of the CI Minutes initiative, we need to enable related feature flags by default and remove the associated code.

After that, the system behavior will be controlled via runner cost factors only.

We plan to do it in multiple steps.

• [SRE] Configure shared runners (general purpose, windows, gitlab and gitlab docker) to be public=0/private=1
• [DEV] Sort out with_shared_runners_limit_enabled scope (the note: #218434 (comment 345370625)): - In Maintainer Review - !32648 (merged)
• [DEV] Add internal dev/SRE docs for managing cost factors on .com: !32984 (diffs) => gitlab-com/runbooks!2293 (merged)
• [DEV] (After with_shared_runners_limit_enabled MR is deployed) Enable system-wide ci_minutes_enforce_quota_for_public_projects FF (via chatops)
• [DEV] Enable ci_minutes_track_for_public_projects FF for all projects (via chatops)
• [DEV/SRE] Make sure nothing has changed in system behavior
• [DEV] Prepare an MR_1 to change FFs to be default_enabled in code: !32581 (merged)
• [DEV] Merge an MR_1 to change FFs to be default_enabled in code
• [DEV] Prepare an MR_2 to remove FFs entirely from the codebase: !33046 (merged)
• [DEV] Merge an MR_2 to remove FFs entirely from the codebase: !33046 (merged)
• [DEV/QA] Add QA Track (as discussed on our final rapid-action meeting): created an issue #220816