Add extra validation on Gossip and GRPC certificate input

[jbair06]

Certificates are supposed to end in a newline. Currently, validation exists to ensure that there is a newline at the end of the text. However, an extra precaution would be to ensure that the certificate ends in a single newline, not allowing the user to enter multiple newlines at the end of the certificate.

Gossip CA Cert might already handle this by default, and if not, will likely error out. But the larger concern is the GRPC certificate. If multiple newlines occur at the end of the GRPC certificate, the hash will change, which will cause issues.