enable persistent Chocolatey cache in Windows CI jobs

enable persistent Chocolatey cache in Windows CI jobs

The intention of this change is to accelerate Windows CI jobs, currently one of
the limiting factors on our CI throughput. This change takes a conservative
approach, giving each relevant job its own cache. In theory these jobs could all
share a cache, but the Gitlab docs¹ imply this is only safe if only a single job
has a `push` policy. To do this effectively, we would probably have to create a
new preliminary CI job that only built the cache. Then all other jobs would
become `pull` consumers of this cache. Perhaps an improvement to make in future.

Closes #2143.

¹ https://docs.gitlab.com/ee/ci/yaml/index.html#cachepolicy