Support envoy 1.14.2, 1.13.2, 1.12.4

[hanshasselberg]

Checklist

• Run the full Envoy integration test using the new versions:

make test-envoy-integ ENVOY_VERSIONS="1.14.2"
make test-envoy-integ ENVOY_VERSIONS="1.13.2"
make test-envoy-integ ENVOY_VERSIONS="1.12.4"

• Update ENVOY_VERSION in test/integration/connect/envoy/run-tests.sh to the latest version
• 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 list of envoy-integration-test-* jobs in the test-integrations workflow to match the new job names changes above.
• Update -envoy-version to the latest version in website/pages/docs/commands/connect/envoy.mdx and defaultEnvoyVersion in command/connect/envoy/envoy.go
• Update the supported versions list in the docs in website/pages/docs/connect/proxies/envoy.mdx
• Update the default envoy version in the golden master files in command/connect/envoy/testdata/* (with find command/connect/envoy/testdata/ -type f -name "*.golden" | xargs sed -i '' 's/1.14.1/1.14.2/g' on OSX)
• Create a PR for consul-k8s to update the default Envoy image to be the latest supported version. It's currently here: https://github.com/hashicorp/consul-k8s/blob/f75b6f559fae9f96667820796edd47c0c7a3824b/connect-inject/handler.go#L23 but probably worth checking the code base and updating this list if there are other references: Update envoy and consul versions consul-k8s#273.
• Create PR for consul-helm to update the default Envoy image. Currently https://github.com/hashicorp/consul-helm/blob/master/values.yaml#L609 but again grep and sanity check: Update comments to match consul-k8s envoy version consul-helm#490.
• Create an issue for Nomad to update the default Envoy docker image they use in their integration with a link to the PR and information about the version we will make the change in and the expected timeline for release: Consul will support envoy 1.14.4 with Consul 1.8 nomad#7665 (comment).

[banks]

LGTM! Great job!

The go-test failure thought seems unlikely to be a flake - a newline is missing from the generated bootstrap config but I don't see changes in this PR that would have broken that 🤷