ssh: add envoy configuration (#5659)

## Summary

Adds the envoy listener config logic for ssh.

## Related issues

<!-- For example...
- #159
-->

## User Explanation

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change doesn't create any user-facing changes, you can leave
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## Checklist

- [ ] reference any related issues
- [ ] updated unit tests
- [ ] add appropriate label (`enhancement`, `bug`, `breaking`,
`dependencies`, `ci`)
- [ ] ready for review

config/policy.go

@@ -930,6 +930,11 @@ func (p *Policy) IsUDPUpstream() bool {
 	return len(p.To) > 0 && p.To[0].URL.Scheme == "udp"
 }
 
+// IsSSH returns true if the route is for SSH.
+func (p *Policy) IsSSH() bool {
+	return len(p.From) > 0 && strings.HasPrefix(p.From, "ssh://")
+}
+
 // AllAllowedDomains returns all the allowed domains.
 func (p *Policy) AllAllowedDomains() []string {
 	var ads []string