remove keyserver in gpg.conf and include dirmng.conf (CVE-2019-13050)

[lestephane]

As described in https://gist.github.com/rjhansen/67ab921ffb4084c865b3618d6955275f

the mitigations includes

1. Open gpg.conf in a text editor. Ensure there is no line starting with keyserver.
   If there is, remove it.
2. Open dirmngr.conf in a text editor. Add the line keyserver hkps://keys.openpgp.org
   to the end of it.

So at the very least, the gpg.conf file needs reviewing. I'm looking for a good known configuration with sane defaults, came up empty so far.

[rolandog]

@lestephane, have you found another source on a more up-to-date and hardened gpg.conf file?