gitlab runner does not allow custom CA

The gitlab proper pods allow for insertion of custom CAs (see here: https://repo1.dso.mil/platform-one/big-bang/apps/developer-tools/gitlab/-/blob/4.12.9-bb.5/chart/values.yaml#L623)

But the gitlab-runner does not support this option. In environments requiring custom CAs, the gitlab runners are unable to authenticate. Running a curl/git command from the spun up runner pods yields 'SSL_UNAUTHORIZED: Self-signed cert in CA chain.'