Emissary should verify that TLS secrets contain valid PEM

[kflynn]

If you point a TLSContext at a secret containing bogus junk, Emissary will happily try to use it, but Envoy validation will fail. There's no real point in allowing Emissary to pass such a broken secret to Envoy -- we can, and should, validate it syntactically before attempting to use it at all.

[khussey]

This has been addressed in Emissary-ingress 2.2, which is now available.