Allow to use custom OpenSSL version

[j-schultz]

Describe the feature you'd like supported

OpenSSL is a complex dependency, and in many projects it is actually a dependency of multiple packages. As a critical component, it is important to keep OpenSSL up-to-date. Hence, we want each one of our dependencies to link against the same OpenSSL version that we supply, to avoid the danger of one package shipping its own potentially outdated and vulnerable OpenSSL version, and having to wait for each individual package to update its dependencies. This also helps when statically linking dependencies, because you cannot easily statically link two different versions of the same library.

Proposed solution

I propose that msquic adds a possibility for OpenSSL (and potentially also for other vendored components) for the user to choose how to find OpenSSL:

• Use submodule
• Supply OPENSSL_LIB_DIR and OPENSSL_INCLUDE_DIR variables
• Use find_package

Additional context

See #5166