Make cdn_ssl_version a Setting
Currently the SSL version used to talk to the CDN can be set via cdn_ssl_version. This exists for proxies that don't support modern standards like TLS 1.2. In an ideal world these proxies wouldn't exist.
It's used here:
The installer has a parameter for this:
Since this is not critical to be set at installation time and can actually be a runtime setting, a database Setting would be a better place.