MSYS2 build automated using Github Actions

[teeks99]

PLEASE NOTE the following text from the iperf3 license. Submitting a
pull request to the iperf3 repository constitutes "[making]
Enhancements available...publicly":

You are under no obligation whatsoever to provide any bug fixes, patches, or
upgrades to the features, functionality or performance of the source code
("Enhancements") to anyone; however, if you choose to make your Enhancements
available either publicly, or directly to Lawrence Berkeley National
Laboratory, without imposing a separate written license agreement for such
Enhancements, then you hereby grant the following license: a non-exclusive,
royalty-free perpetual license to install, use, modify, prepare derivative
works, incorporate into other computer software, distribute, and sublicense
such enhancements or derivative works thereof, in binary and source code form.

The complete iperf3 license is available in the LICENSE file in the
top directory of the iperf3 source tree.

• Version of iperf3 (or development branch, such as master or
  3.1-STABLE) to which this pull request applies:

  master

• Issues fixed (if any):
  none

• Brief description of code changes (suitable for use as a commit message):

  MSYS2 build automated using Github Actions

  This will detect any build failures for windows/msys as well as creating a .zip package that is able to be consumed.

[teeks99]

This may also require an administrator to go set Settings -> Actions -> Allow All Actions.

You can see what it looks like in the forked repo.