(PE-5503) Added -pem to end of function names to clarify intent

This commit changes the name of the `get-x509s-from-ssl-cert` function
to `get-x509s-from-ssl-cert-pem` and the name of the
`get-x509s-from-ssl-cert-chain` function to
`get-x509s-from-ssl-cert-chain-pem` in order to make the intention of
the supplied arguments to each a little more obvious.