Clean documents and dev-overrides

With changes from passthrough, istio-operatorless, removal of packages (promtail), etc our docs and dev-override examples need to be updated.

Some things to look out for while updating:

• Remove istio and istioOperator and replace it with istioGateway if needed
• Remove promtail, thanos, jaeger from test files
• Update DEVELOPMENT_MAINTENANCE.md to include new chart updating instructions, removing all mentions of kpt.
• Update DEVELOPMENT_MAINTENANCE.md to include upstream key if there any any example values.yaml
• Update DEVELOPMENT_MAINTENANCE.md to remove 'Modifications made to upstream chart' section if the information is no longer accurate.
• Test and make sure the dev-override minimal.yaml and xxx-testing.yaml work

• Add upstream repo as comment within values.yaml. Example: https://repo1.dso.mil/big-bang/product/packages/istiod/-/blob/main/chart/values.yaml?ref_type=heads#L98