Document that gRPC traffic requires a cert

[stabai]

Problem

The fact that using http2 traffic like gRPC requires a cert is not explicitly mentioned in the gRPC example page. This is confusing, because requiring an https context for gRPC is not expected.

Proposed documentation

Explicitly state that the TLS certificate is NECESSARY in one of the sections talking about the ingress config. If there are any workarounds for this issue, presenting them there would also be ideal.

/kind documentation /remove-kind feature