Misc CI fixes

[0x00002a]

This makes some minor changes to the CI and build files so that it will now pass in every tested environment. Note that it does remove mingw compilation because the choco package for 10.2.0 lacks thread support and 8.1.0 can't compile this library (doesn't support enough 20). I tried setting up msys2 instead but it still used the default installed gcc (8.1.0) and I'm not sure how to fix that. I can add it back if needed but having a CI run that always fails due to external problems rather than an issue with the library itself is not very useful imo.

Main changes:

• The boost define and various compiler flags needed are now wrapped in a cmake function called for tests, malloy-objs, and the examples
• The CI now runs on any branch being pushed (this is mostly for the benefit of forks)
• The client tls example is now build conditional on TLS being enabled
• openssl is now linked to publicly. This is similar to #9 in that it worked when the headers were in the system path, but not when specified by cmake (e.g. in the case of msvc using choco openssl).

The result is that the CI passes and therefore this library and its examples can be built with boost version 1.74.0 through 1.76.0 with or without tls on gcc-11 and the latest (stable) msvc.

[Tectu]

Note that it does remove mingw compilation because [...]

Can we keep the tests in the workflow file but keep them disabled / commented out and have this as a comment in there? This way we can easily re-enable them in the future once the available packages are have been updated to support the necessary features.

[Tectu]

Great stuff, thanks a lot!