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
this blank. If filled out, add the `docs` label -->

## Checklist

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

config/policy_test.go

@@ -460,6 +460,14 @@ func TestPolicy_IsTCPUpstream(t *testing.T) {
 	assert.False(t, p3.IsTCPUpstream())
 }
 
+func TestPolicy_IsSSH(t *testing.T) {
+	p1 := Policy{From: "https://example.com"}
+	assert.False(t, p1.IsSSH())
+
+	p2 := Policy{From: "ssh://example.com"}
+	assert.True(t, p2.IsSSH())
+}
+
 func mustParseWeightedURLs(t testing.TB, urls ...string) WeightedURLs {
 	wu, err := ParseWeightedUrls(urls...)
 	require.NoError(t, err)