Drone: Add Windows PR pipeline (#26589)

* Drone: Add Windows PR pipeline
* CI: Add Dockerfile for WiX image

scripts/build/ci-wix/Dockerfile

@@ -0,0 +1,18 @@
+# This has to correspond to the version the Drone runners have
+FROM mcr.microsoft.com/windows:1809
+
+WORKDIR C:\\App
+
+RUN powershell Set-ExecutionPolicy RemoteSigned -Scope CurrentUser -Force
+RUN powershell Invoke-Expression (New-Object System.Net.WebClient).DownloadString('https://get.scoop.sh')
+RUN scoop install wixtoolset@3.11.2
+RUN powershell (New-Object Net.WebClient).DownloadFile(\
+  \"https://grafana-downloads.storage.googleapis.com/ci-dependencies/nssm-2.24.zip\", \
+  \"nssm-2.24.zip\")
+RUN scoop install git@2.28.0.windows.1
+RUN scoop bucket add extras
+RUN scoop install gcloud@305.0.0
+# Installing dos2unix fails if not under PowerShell
+RUN powershell scoop install dos2unix
+
+ENTRYPOINT ["powershell"]