Adds Helm Post-Install Hook

Adds a Helm post-install hook so the chart properly reflects IstioOperator status. Uses image "registry1.dso.mil/ironbank/big-bang/base:8.4" since it contains the kubectl client needed to check Istiod deployment status. Note that the istio-operator namespace/service account is used since the istio-system/istiod service account does not have the necessary RBAC permissions to watch the Istiod deployment rollout status.

Requires: https://repo1.dso.mil/platform-one/big-bang/apps/core/istio-controlplane/-/merge_requests/76

Fixes: #54 (closed)

xref: https://repo1.dso.mil/platform-one/big-bang/bigbang/-/issues/587

cc: @stas @michaelmcleroy