Specify allowed ingress gateway protocols in docs

[jackloughran]

It seems like only tls and http are supported right now.

consul/agent/structs/config_entry_gateways.go

Lines 37 to 40 in 586ee25

	// Protocol declares what type of traffic this listener is expected to
	// receive. Depending on the protocol, a listener might support multiplexing
	// services over a single port, or additional discovery chain features. The
	// current supported values are: (tcp | http).

consul/agent/structs/config_entry_gateways.go

Lines 123 to 126 in 586ee25

	validProtocols := map[string]bool{
	"http": true,
	"tcp": true,
	}

I found this confusing when I was going through it. I'm hoping this will make someone else's life easier.

[hashicorp-cla]

All committers have signed the CLA.

[freddygv]

Thanks for the PR, this request seems reasonable to me.

Requesting one edit.

[freddygv]

LGTM!

[hashicorp-ci]

🍒✅ Cherry pick of commit 77d0c33 onto stable-website succeeded!