artifacts: Windows CI Installer

* Windows CI Installer

This PR introduces CI builds of a windows installer(using NSIS) .

It builds an executable that installs Etherpad and runs it.

There are obvious steps to make once this has been merged. But I'd suggest on each release we include both the .zip and the .exe and allow users to have a portable zip or an installed executable.

https://github.com/ether/etherpad_nsis

This was a relatively rushed project (4 hours) and I didn't want to spend any more time on it so it will need a foster parent to maintain it :)

props to @joncloud for https://github.com/joncloud/makensis-action-test and the nsis team that while have a horrible UX make relatively easy to use and rapid tools.

Note for review: I'm using linux to build the windows executable, this may need to be reviewed and we might want to switch to Windows if we can confirm building on linux causes a problem.

* CI: Use Windows to build the .zip

.github/workflows/windows-installer.yml

@@ -0,0 +1,61 @@
+name: "Windows Installer"
+
+# any branch is useful for testing before a PR is submitted
+on: [push, pull_request]
+
+jobs:
+  build:
+    # run on pushes to any branch
+    # run on PRs from external forks
+    if: |
+         (github.event_name != 'pull_request')
+         || (github.event.pull_request.head.repo.id != github.event.pull_request.base.repo.id)
+
+    name: Build Zip & Exe
+    runs-on: windows-latest
+
+    steps:
+    - uses: msys2/setup-msys2@v2
+      with:
+        path-type: inherit
+        install: >-
+          zip
+
+    - name: Checkout repository
+      uses: actions/checkout@v2
+
+    - uses: actions/setup-node@v2
+      with:
+        node-version: 12
+
+    - name: Install all dependencies and symlink for ep_etherpad-lite
+      shell: msys2 {0}
+      run: src/bin/installDeps.sh
+
+    - name: Run the backend tests
+      shell: msys2 {0}
+      run: cd src && npm test
+
+    - name: Build the .zip
+      shell: msys2 {0}
+      run: src/bin/buildForWindows.sh
+
+    - name: Extract the .zip into folder
+      run: 7z x etherpad-lite-win.zip -oetherpad-lite-new
+
+    - name: Grab nsis config
+      run: git clone https://github.com/ether/etherpad_nsis.git
+
+    - name: Create installer
+      uses: joncloud/makensis-action@v3.4
+      with:
+        script-file: 'etherpad_nsis/etherpad.nsi'
+
+    - name: Check something..
+      run: ls etherpad_nsis
+
+    - name: Archive production artifacts
+      uses: actions/upload-artifact@v2
+      with:
+        name: etherpad-server-windows.exe
+        path: etherpad_nsis/etherpad-server-windows.exe