DialTLS specifies an optional dial function for creating TLS connections for non-proxied HTTPS requests.

If DialTLS is nil, Dial and TLSClientConfig are used.

If DialTLS is set, the Dial hook is not used for HTTPS requests and the TLSClientConfig and TLSHandshakeTimeout are ignored. The returned net.Conn is assumed to already be past the TLS handshake.