add namespace toggle to tproxy

[kschoche]

Changes proposed in this PR:

• Adds ability to define default tproxy mode settings at the k8s namespace level.
• renames tproxy annotation to "consul.hashicorp.com/transparent-proxy-default"

How I've tested this PR:
Unit tests, manual testing via deploying a simple counting service with no tproxy annotations set, then toggling the namespace label true/false and redeploying:

% kubectl describe pod counting | grep redirect
      # Apply traffic redirection rules.
      /consul/connect-inject/consul connect redirect-traffic \
% kubectl get namespaces --show-labels| grep transparent
default           Active   261d   consul.hashicorp.com/transparent-proxy=true
% kubectl delete -f svc.yaml
service "counting" deleted
serviceaccount "counting" deleted
pod "counting" deleted
% kubectl label namespace default consul.hashicorp.com/transparent-proxy=false --overwrite
namespace/default labeled
% kubectl apply -f svc.yaml
service/counting created
serviceaccount/counting created
pod/counting created
% kubectl describe pod counting | grep redirect
%

NOTE: hashicorp/consul-helm#942 must be merged in order to support this.

How I expect reviewers to test this PR:
Unit tests, manual test

Checklist:

• Tests added
• CHANGELOG entry added (HashiCorp engineers only, community PRs should not add a changelog entry)

[kschoche]

We now pass the namespace into containerInit from the handler, this allows us to (1) re-use the transparentProxyEnabled() function between containerInit/endpointsController and (2) makes testing simpler so we do not need to load up a k8s clientset for every containerInit test.

[thisisnotashwin]

This looks really great!! Have a few suggestions for improvements!!

[thisisnotashwin]

Given this a change in consul-k8s, can you rephrase the connectInject.transparentProxy.defaultEnabled helm value as the equivalent flag and sub-command it gets set on in consul-k8s?
Additionally, I'd phrase it as annotation on the Pod and label on the Namespace. I don't think pod annotation and namespace label seem accurate.
Conversely:
Setting the annotations consul.hashicorp.com/transparent-proxy to true/false on the pod will define whether tproxy is enabled/disabled for the pod. Maybe?

[ndhanushkodi]

Looks great Kyle!!

[thisisnotashwin]

great work bud!!