Resolve "Add missing `envoyFilters` templating"

General MR

Summary

This MR adds the ability to deploy EnvoyFilter resources with istiod via additionalEnvoyFilters.

Testing Procedure

1. Deploy Big Bang with this overlay:

istio:
  enabled: false

istioOperator:
  enabled: false

istioCRDs:
  enabled: true

istiod:
  enabled: true
  git:
    tag: null
    branch: 27-add-missing-envoyfilters-templating
  values:
    additionalEnvoyFilters:
      - name: hello-world
        labels:
          hello: world
        annotations:
          hello/world: "true"
        spec:
          configPatches:
            - applyTo: HTTP_FILTER
              match:
                context: SIDECAR_INBOUND
                listener:
                  filterChain:
                    filter:
                      name: envoy.filters.network.http_connection_manager
                      subFilter:
                        name: envoy.filters.http.router
              patch:
                operation: INSERT_BEFORE
                value:
                  name: envoy.filters.http.lua.hello-world
                  typed_config:
                    "@type": type.googleapis.com/envoy.extensions.filters.http.lua.v3.Lua
                    inlineCode: |
                      function envoy_on_response(response_handle)
                        response_handle:headers():add("x-hello", "world")
                      end

istioGateway:
  enabled: true

2. Verify the EnvoyFilter gets created:

❯ kubectl get envoyfilters -n istio-system hello-world
NAME          AGE
hello-world   28m

3. Verify the EnvoyFilter gets pushed to your workload:

❯ istioctl pc all -n monitoring prometheus-monitoring-monitoring-kube-prometheus-0 -o yaml | grep hello-world
              - name: envoy.filters.http.lua.hello-world
              - name: envoy.filters.http.lua.hello-world
              - name: envoy.filters.http.lua.hello-world

4. Verify the EnvoyFilter does the thing:

❯ curl -v https://prometheus.dev.bigbang.mil/ 2>&1 | grep x-hello
< x-hello: world

Linked Issue

#27 (closed)

Upgrade Notices

N/A