Add templating to provide more specific network policies

[blancharda]

Overview

The current network policy egress routes allow for remoteGenerated: Anywhere on almost all gitlab pods. We should enable more restrictive egress policies by adding helm values and corresponding templates to allow a user to customize more limited egress for their specific environment.

See more discussion here

Proposal

• Identify points of egress (database, storage, redis... other?) and map them to each gitlab pod
• Add individual egress rules for each mapping
• By default, perhaps we continue to allow traffic anywhere so that network policies don't break an initial install
• Template the destination to allow for a custom CIDR (once this is implemented) // pod selector + namespace // other destination?
• Consider something like values.additionalNetworkAllows[] to allow a user to specify fully custom additional rules

[blancharda]

Duplicates #78

[zachariahmiller]

@blancharda Appreciate you!