Only add SSLProxyEngine in proxy mode and when SSL is enabled for the web (fixes #6269)

SSLProxyEngine is neither needed for http(s) redirects nor for non-SSL proxy configs.
Thus excluding it from these cases.

Based on a fix by Thom <>
1 job for !1549 with 6269-redirects-render-invalid-apache-config-on-non-ssl-web-server-since-mr-1521-jdsn in 7 minutes and 11 seconds (queued for 7 seconds)
merge request