Consider adding Windows support to our a8c-ci-toolkit plugin

[AliSoftware]

Now that we're starting to have project which are building on Windows agents (esp. Desktop apps like Studio, etc), it would be useful if we can confirm that the generic helpers from a8c-ci-toolkit (e.g. save_cache, hash_file, …) are able to be used on Windows agents too, and if not, make them Windows-compatible.

We'll first need to check:

• If our Windows agent already have bash support built-in (maybe everything already works already? We just haven't tested it yet)
• Or if the calls to any a8c-ci-toolkit-buildkite-plugin/bin helper needs to be wrapped in a .ps1 PowerShell script that would run them in a bash container or something…
• Or if we'll need to translate each of our helpers in .ps1 (thus having two copies of each helper, one written in .ps1 and one in bash?)

[AliSoftware]

💡 If we end up adding ps1 scripts for Windows in this plugin, we might want to look at at tool like PSScriptAnalyzer to lint our .ps1 scripts on CI, similar to how we use shellcheck to lint our bash scripts for Linux/Mac.

(See also official doc of the tool, PSScriptAnalyzer GitHub repo, Docker image repo, Docker image on DockerHub

[mokagio]

Related #132