Use colcon builds on windows for ign-plugin

[scpeters]

Part of #412. While adding a dependency on ign-utils to ign-plugin in gazebo-tooling/gazebodistro#43 for gazebosim/gz-plugin#55, we may as well switch to colcon at the same time.

[scpeters]

testing:

• https://build.osrfoundation.org/job/_dsl_ignition/1178/

Added items:
    GeneratedJob{name='ign_plugin-pr-win'}
    GeneratedJob{name='ign_plugin-ign-1-win'}
    GeneratedJob{name='ign_plugin-ci-win'}
...
Unreferenced items:
    GeneratedJob{name='ignition_plugin-ci-ign-plugin1-windows7-amd64'}
    GeneratedJob{name='ignition_plugin-ci-main-windows7-amd64'}
    GeneratedJob{name='ignition_plugin-ci-pr_any-windows7-amd64'}
Disabled items:
    GeneratedJob{name='ignition_plugin-ci-main-windows7-amd64'}
    GeneratedJob{name='ignition_plugin-ci-ign-plugin1-windows7-amd64'}
    GeneratedJob{name='ignition_plugin-ci-pr_any-windows7-amd64'}

• https://build.osrfoundation.org/job/_dsl_ignition_collection/383/

[scpeters]

another test:

• https://build.osrfoundation.org/view/ign-citadel/job/ign_plugin-ign-1-win/1/