Implement ability to control ServiceAccount behaviors

Summary

Split from #2033 (closed)

Implement the ability to configure, possibly generate, the ServiceAccount used by each of our charts.

Having the ability to configure these items allows the use of RBAC & IAM based behaviors from various sources, including Vault (#2033 (closed)) and AWS (#1832 (closed))

Current behavior

The sub-chart components under gitlab/* can not be configure to use a specific ServiceAccount.

Expected behavior

Ability to configure ServiceAccount of deployed charts.