* Extract class for building SSL context
This commit extracts the `MiniSSL::Context` creation into its own
`MiniSSL::ContextBuilder` class along the same lines as in [#1989].
This will allow us to reuse this code for adding SSL support to the
control app (issue [#2015]). Since we will need the `MiniSSL` require
and check in both places, I moved that into the `ContextBuilder` class
as well.
[#1989]: https://github.com/puma/puma/pull/1989
[#2015]: https://github.com/puma/puma/pull/2015
* Add SSL support for the control app
This starts to address [#2015]. I think we will need to add SSL support
to the control cli as well.
[#2015]: https://github.com/puma/puma/issues/2015
