The default is openssl.cnf  The project seems to prefer xxx.conf these
days, but we should use the default convention.

Rename all foo.conf (except for Configurations) to foo.cnf

Fixes #11174
Reviewed-by: NPaul Yang <kaishen.yy@antfin.com>
Reviewed-by: NTomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/11176)