mod_proxy/ssl: Proxy SSL client certificate

configuration and other proxy SSL configurations
broken inside <Proxy> context.
PR 63430
Triggered by r1855646+r1855748.
Patch from rpluem (proxy) and ylavic (ssl).


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1859371 13f79535-47bb-0310-9956-ffa450edef68