[CMAKE] Pull miniupnpc windows library dependencies in the find module

Summary:
This is quite identical to what is done with libevent. It prevents from
managing the dependencies at the project level.

The definitions are kept at project level since there are assuming that
we build using the depends, which should always be the case for now but
is not a library requirement. A comment is added to explain this.

Depends on D5576.

Test Plan:
Build for windows. Run the binaries and check the UPnP functions are
available.

Run the windows Gitian build.

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D5575