Allow setting TLS for gRPC with deprecated options [1.13.x]

[freddygv]

Replaces #14644.

This PR is only being merged against release/1.13.x because it is not needed in Consul 1.14.

Once 1.14 is released we will drop support for configuring TLS for gRPC using the flags available in Consul 1.11.

Description

Currently TLS for gRPC can only be enabled using the options nested in the tls.grpc configuration stanza.

That leads to a breaking change where the TLS options deprecated in 1.12 cannot be used to enable TLS for gRPC.

This commit updates the logic for determining whether TLS should be used on the public gRPC port: If the 1.12 tls stanza is not specified we default to the original behavior, which is to enable TLS for gRPC if the HTTPS port is set.

The change allows for consul-k8s to continue to use TLS flags compatible with 1.11 until 1.14 is released.

Testing & Reproduction steps

• Unit tests
• Manual tests:
  • Given multiple config files where some use the TLS stanza and others don't --> used post 1.13 logic to set TLS since at least one specified the new TLS stanza.
  • Given multiple config files where TLS certs were specified with deprecated flags and the HTTPS port was set --> used old logic and enabled TLS

Links

Related to:

• Consul 1.13 cant disable TLS for gRPC Server when AutoEncrypt is in use (backwards compatibility & envoy usage broken) #14253
• server: ensure peer replication can successfully use TLS over external gRPC #13733

PR Checklist

• updated test coverage
• external facing docs updated
• not a security concern