connect: add support for envoy 1.16.0, drop support for 1.12.x, and bump point releases as well

[rboyer]

(Backports will be handled separately as each major release runs different supported verisons)

Supported versions will be: "1.16.0", "1.15.2", "1.14.5", "1.13.6"

• In the correct release branch update the default ENVOY_VERSION value in run-tests.sh. It should contain the new version
• update the supported version list baked into the agent self endpoint which is shared for the xds golden tests
• regenerate the golden test outputs and delete any for older versions that have rolled off the list
• Update the CI jobs in .circleci/config.yml. There are multiple jobs named envoy-integration-test-* where the oldest has a full definition while the others are aliases that just change the version number.
  • Update the version numbers such that they match the new supported list.
  • Update the list of envoy-integration-test-* jobs in the test-integrations workflow to match the new job names changes above.
• Update the supported versions list in the docs in website/source/connect/proxies/envoy.md
• Create a PR for consul-k8s to update the default Envoy image to be the latest supported version. Consul will support envoy 1.16.0 with Consul 1.9 consul-k8s#303
• Create PR for consul-helm to update the default Envoy image. Consul will support envoy 1.16.0 with Consul 1.9 consul-helm#562
• Create an issue for Nomad to update the default Envoy docker image they use in their integration

[freddygv]

LGTM

@rboyer Where does the checklist in the PR comment live? I think the second item should be updated to reflect the new location of EnvoyVersions

[rboyer]

LGTM

@rboyer Where does the checklist in the PR comment live? I think the second item should be updated to reflect the new location of EnvoyVersions

The checklist is somewhere in google docs and it's already quite out of date. I think @mikemorris was going to move it somewhere to live with the "how to add config" blob, but I don't know the status of that.