Remove BB created servicemonitor and enable upstream ones

Currently Gitlab uses a Big Bang created service monitor - https://repo1.dso.mil/platform-one/big-bang/apps/developer-tools/gitlab/-/blob/main/chart/charts/gitlab/charts/gitlab-exporter/templates/bigbang/service-monitor.yaml

With the 14.9.2 update the upstream Gitlab chart is now capable of creating service and pod monitors for a number of metrics endpoints. We should make sure that these are conditionally enabled (when monitoring is enabled at the BB level).

AC:

• Big Bang created servicemonitor deleted
• Gitlab upstream monitors conditionally enabled when monitoring is enabled
• All targets showing as up/healthy in Prometheus (may require network policy changes)