feat(istio): added iterable gateways

Package Merge Request

Package Changes

This MR enables an iterable pattern for defining istio gateways that DRYs up our operatorless gateway implementation and allows the customer to easily define their own custom gateways without an additional HelmRelease. Variations on how the pattern can be used are fully documented in the big bang values.yaml

Additionally I made some changes to the basePackage schema to support more advanced post-renderer support for the pattern. Now postRenderers can be fed an array of post-renderer objects (the classic way) or it can be given a map of keys to arrays. The keys correspond to different gateways. This allows customers to define different post-renderers for each of their gateway configurations. This pattern is documented in the comments of the values.yaml.

One last significant change is I'm using YAML anchors so we can stop repeating ourselves when defining our *.dev.bigbang.mil cert bundle.

Package MR

N/A

For Issue

Closes #2507 (closed)

Upgrade Notices

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