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?
Well, by default, all are set to AUTO, as you indicated. However, when actually coding in C++ there are calls to many functions that take an additional parameter that allows the dev to indicate _which_ plugin provider to use. This is because several providers can handle the same request. If the dev doesn't do that, then QCA does some auto-selection which may not be what you want.

Ensuring plugins (except qca-ossl) are not built unless explicitly defined, helps not only with that circumstance, but also with general Homebrew install usage, where one plugin that fails to build (in the future, not right now) causes an overall source build/install to fail for a user, even if that particular plugin is not even needed. Even setting all dependencies to `:recommended` would still help with selection of which plugins get installed, and be better than leaving it up to AUTO.

Also, if everything is left as AUTO, how would the Homebrew user know which plugins were or were not installed (other than installing in verbose mode)?