Implement ability to control ServiceAccount behaviors
Summary
Split from #2033
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) and AWS (#1832)
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.