ci: woodpecker: add exec pipeline

.woodpecker/exec.yml

@@ -0,0 +1,23 @@
+pipeline:
+  test:
+    image: bash
+    commands:
+    - "nix run 'nixpkgs#hello'"
+
+  notify:
+    image: bash
+    secrets:
+    - source: matrix_homeserver
+      target: address
+    - source: matrix_roomid
+      target: room
+    - source: matrix_username
+      target: user
+    - source: matrix_password
+      target: pass
+    commands:
+    - nix run 'github:ambroisie/matrix-notifier'
+    when:
+      status:
+      - failure
+      - success