[Cells 1.0] Decide what to do with `secrets.ci_jwt_signing_key`
Decide what to do with this secret with respect to Cells.
Options:
- Remove this secret as it is un-used
- Per cell
- Ensure it is the same for all cells
- Something else
Note, https://docs.gitlab.com/ee/development/application_secrets.html#secret-entries says, but we actually intend to rename it in #428129:
The base key for encrypting the CI_JOB_JWT and CI_JOB_JWT_V2 predefined CI/CD variables. CI_JOB_JWT and CI_JOB_JWT_V2 were deprecated in GitLab 15.9 and are scheduled to be removed in GitLab 17.0.
Edited by Thong Kuah