Updated Docker file to build Ops Agent Windows tarball.

[XuechunHou]

Description

This PR added additional steps in the Windows dockerfile, to also build Ops Agent UAP Plugin tarball for Windows.

Related issue

b/399401166

How has this been tested?

That it generates a tarball and includes everything expected.
It's accessible in kokoro presubmit tests: https://screenshot.googleplex.com/BRji5xWz9R4QwGd

Checklist:

• Unit tests
  • Unit tests do not apply.
  • Unit tests have been added/modified and passed for this PR.
• Integration tests
  • Integration tests do not apply.
  • Integration tests have been added/modified and passed for this PR.
• Documentation
  • This PR introduces no user visible changes.
  • This PR introduces user visible changes and the corresponding documentation change has been made.
• Minor version bump
  • This PR introduces no new features.
  • This PR introduces new features, and there is a separate PR to bump the minor version since the last release already.
  • This PR bumps the version.