Rename the PROVIDER_CONF trace to CONF

Other configuration modules may have use for tracing, and having one
tracing category for each of them is a bit much.  Instead, we make one
category for them all.

Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/8680)