Add DH params for httpd to certbot_extra_formats

[razorsedge]

Add support for adding custom Diffie-Hellman parameters for Apache httpd.

I do this in a renewal-hooks/deploy script:
cat ${RENEWED_LINEAGE}/cert.pem /etc/pki/tls/certs/dh2048.pem >/etc/pki/tls/certs/http-${DOMAIN}.crt

This is for when you are running older versions of httpd and cannot use httpd's SSLOpenSSLConfCmd option.
# Apache (2.4.8 and newer) and OpenSSL 1.0.2 or later
#SSLOpenSSLConfCmd DHParameters "/etc/pki/tls/certs/dh2048.pem"

[tallero]

Added in this commit.
Please test it if you can.