fix(nd-common): support istio-proxy native sidecar (initContainer) preStop override

[schahal]

Why

Context

Kubernetes native sidecar containers run as InitContainers

Istio allows us to run the proxy as a native sidecar.

What This Change Does

Allows preStop commands to be set on initContainers as well.

But Why Is This Change Needed?

Ideally, the default /drain on native sidecars should suffice.

However, an open bug (istio/istio#51855) is forcing us to potentially bring our default preStop commands on the native sidecars as well.

Diffs

Diff between default values and setting istio.nativeSidecarsEnabled: true

When to use: This is the proposed ideal setting when we want a workaround to istio/istio#51855

@@ -234,7 +234,7 @@
         traffic.sidecar.istio.io/excludeInboundPorts: "9090"
         proxy.istio.io/overrides: >-
           {
-            "containers": [
+            "initContainers": [
               {
                 "name": "istio-proxy",
                 "lifecycle": {

Diff between default values and setting istio.nativeSidecarsEnabled: true and preStopDefaultEnabled: false

When to use: This is the proposed ideal setting when istio/istio#51855 is fixed and we want to default to upstream/Istio's drain mechanism... i.e., no override

@@ -232,25 +232,6 @@
         checksum/secrets: c8fa9ff9cda8a0e2d93fdc712c82373c94a1a5f1a48fc6d8db9f978047d937b6
         proxy.istio.io/config: '<redacted>'
         traffic.sidecar.istio.io/excludeInboundPorts: "9090"
-        proxy.istio.io/overrides: >-
-          {
-            "containers": [
-              {
-                "name": "istio-proxy",
-                "lifecycle": {
-                  "preStop": {
-                    "exec": {
-                      "command": [
-                        "/bin/sh",
-                        "-c",
-                        "while [ $(netstat -plunt | grep tcp | egrep -v 'envoy|pilot-agent' | wc -l | xargs) -ne 0 ]; do sleep 1; done"
-                      ]
-                    }
-                  }
-                }
-              }
-            ]
-          }
         ad.datadoghq.com/simple-app.check_names: '["prometheus"]'
         ad.datadoghq.com/simple-app.init_configs: '[{}]'
         ad.datadoghq.com/simple-app.instances: |-