support disabling mTLS

[ripienaar]

To do this we need to support a blank ca certificate

aaasvc/cmd/run.go

Lines 63 to 69 in 07eabc0

	if conf.TLSCertificate == "" || conf.TLSKey == "" || conf.TLSCA == "" {
	return fmt.Errorf("TLS settings are not set")
	}
	server.TLSCertificate = flags.Filename(conf.TLSCertificate)
	server.TLSCertificateKey = flags.Filename(conf.TLSKey)
	server.TLSCACertificate = flags.Filename(conf.TLSCA)