feat: upgrade Windows support to "feature" (#778)

Issue #, if available:

*Description of changes:*
Now that all infra/CI is setup and has been working stably for a few
weeks, its time to mark Windows as a new "feature" so we can update
Finch's next version number for the next release (tracked at #748).

Original Windows PR for reference:
#649.

*Testing done:*



- [x] I've reviewed the guidance in CONTRIBUTING.md


#### License Acceptance

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 license.

Signed-off-by: Justin Alvarez <alvajus@amazon.com>