Add simple TLS cert validation test for remote relay endpoints

[englishm-cloudflare]

Idea from @kixelated - it would be useful to have a test that shows which remote relay endpoints have valid certs.

[englishm-cloudflare]

Basic idea here is that instead of having tls_disable_verify as a hard-coded config setting, we should run a separate test that just checks for a valid cert and gives a pass/fail on that and then runs the remaining tests with tls_disable_verify set depending. That way we can get a signal if certs have expired, etc. and also have more useful endpoints that can be used by browser-based implementations (where it's much more challenging to work around invalid certs).