Livepeer.Cloud SPE - add windows build

[mikezupper]

What does this pull request do? Explain your changes. (required)
This provides a docker build for Windows binaries. This was in response to the Bounty published by @rickstaa
livepeer/bounties#62

Specific updates (required)

• added a Makefile entry for docker-windows
• added a Dockerfile.windows file

How did you test each of these updates (required)
The build ran successfully on Livepeer.Cloud's CI/CD environment. The windows binary was deployed to a windows server and properly started. (testing on the actual transcoding was NOT done)

Does this pull request close any open issues?
No

Checklist:

• Read the contribution guide
• make runs successfully
• All tests in ./test.sh pass
• README and other documentation updated
• Pending changelog updated

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 31.91887%. Comparing base (8a37cb2) to head (f18c976).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@              Coverage Diff              @@
##              master       #3366   +/-   ##
=============================================
  Coverage   31.91887%   31.91887%           
=============================================
  Files            169         169           
  Lines          41217       41217           
=============================================
  Hits           13156       13156           
  Misses         27071       27071           
  Partials         990         990           

see 2 files with indirect coverage changes

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[hjpotter92]

we were installing libz-mingw-w64-dev in our workflow causing that to take precedence over self-compiled zlib. fixed this behaviour in our build workflow now in #3848