Doc: Fix misleading wording of CRL parameters

Doc: Fix misleading wording of CRL parameters

ssl_crl_file and ssl_crl_dir are both used to for client certificate
revocation, not server certificates.  The description for the params
could be easily misread to mean the opposite however,  as evidenced
by the bugreport leading to this fix.  Similarly, expand sslcrl and
and sslcrldir to explicitly mention server certificates. While there
also mention sslcrldir where previously only sslcrl was discussed.

Backpatch down to v10, with the CRL dir fixes down to 14 where they
were introduced.

Author: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Reviewed-by: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Discussion: https://postgr.es/m/20211202.135441.590555657708629486.horikyota.ntt@gmail.com
Discussion: https://postgr.es/m/CABWY_HCBUCjY1EJHrEGePGEaSZ5b29apgTohCyygtsqe_ySYng@mail.gmail.com
Backpatch-through: 10