Add working groups page and layout

- Provide the script that generate the wg.yaml
- Create a workflow that update the working group yaml periodically
- Add the wg page and layout
- A bit of CSS to make the page looks ok

Author: cescoffier

working-groups/templates/wg.yaml

@@ -0,0 +1,14 @@
+---
+working-groups:
+  {#for board in boards}
+    - title: "{board.title}"
+      board-url: "{board.url}"
+      short-description: {board.shortDescription.trim()}
+      readme: |
+        {board.getIndentedReadme().raw}
+      status: {board.getBadgeText()}
+      last-activity: {board.getLastActivityDate()}
+      {#if board.getLastUpdate()  && board.getLastUpdate().body.trim()}
+      last-update: {board.getLastUpdate().body.trim()}
+      {/if}
+  {/for}