SPIKE: Investigate introducing Helm partial/helpers to DRY umbrella

Currently the Big Bang umbrella contains a number of duplicative patterns and template files. Each package is largely represented the same way with some slight deviations. Ideally we'd have as little duplication as possible to make maintenance easier.

For instance https://repo1.dso.mil/big-bang/bigbang/-/blob/master/chart/templates/grafana contains a GitRepository that looks quite similar to https://repo1.dso.mil/big-bang/bigbang/-/blob/master/chart/templates/loki/gitrepository.yaml. The GitRepository resource could be generated with a _helper.tpl.

One potential option would be to replace all existing files of a particular resource type with a loop like this:

for each enabled package
  generate GitRepository
  generate HelmRelease
  generate Namespace
  generate Secret

There would be some tradeoffs associated with this as it might involve moving some business logic from static files into the _helpers but ultimately I believe it would help surface the (relatively speaking) small amount of logic that actually exists in umbrella.

This relates to &487 in that the structure and metadata in our values.yaml could drastically impact how easily some of the _helpers are written.