Add namespace read support to the connect-inject clusterrole so we can read namespaces

[kschoche]

Add namespace read support to the clusterrole so we can read namespaces in the endpoints controller and webhook.

Changes proposed in this PR:

• Add namespaces get to the connect-inject clusterrole. The webhook handler and the endpoints controller both read namespaces now to fetch metadata related to tproxy labels.

How I've tested this PR:
manually tested alongside hashicorp/consul-k8s#510 and verified that it resolves the following error:

Error from server: error when creating "svc.yaml": admission webhook "kyle-consul-consul-connect-injector.consul.hashicorp.com" denied the request: error getting namespace metadata for container: namespaces "default" is forbidden: User "system:serviceaccount:default:kyle-consul-consul-connect-injector-webhook-svc-account" cannot get resource "namespaces" in API group "" in the namespace "default"

How I expect reviewers to test this PR:
code review

Checklist:

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