👷 Notify new devenv images in penpotdev

Signed-off-by: David Barragán Merino <david.barragan@kaleidos.net>

.github/workflows/build-docker-devenv.yml

@@ -71,4 +71,13 @@ jobs:
           TEXT: |
             🚀 *[PENPOT] New devenv available*
             📄 You may want to update your devenv.
-            @alvaro
+
+      - name: Notify Mattermost (developers)
+        uses: mattermost/action-mattermost-notify@ae31bb6f9e26a54336e79696f108a2c91cf55b4e # v2.1.0
+        with:
+          MATTERMOST_WEBHOOK_URL: ${{ secrets.MATTERMOST_WEBHOOK }}
+          MATTERMOST_CHANNEL: penpotdev
+          TEXT: |
+            🚀 *[PENPOT] New devenv available*
+            📄 You may want to update your devenv.
+            (\cc @alvaro)