qca: add options for head, qt5, tests, api docs and building all plugins

@mikemcquaid Do you think all of the plugins should just be `:recommended` (excepting `qca-ossl` which should always be built), since they all successfully build?
Not sure why that is a concern, since running them is optional. I could instead run `ctest` with an option to exclude that `FileWatch` test, but I don't see why that would be beneficial if someone is willing to debug it.