Add auto publish workflow (#138)

* Add auto publish workflow

* Use SHA

* Trigger on branches

* Fix

* Use main branch

* Fix typo

Author: mosuem

.github/workflows/publish.yml

@@ -0,0 +1,10 @@
+name: Publish
+on:
+  pull_request:
+    branches: [ master ]
+    types: [opened, synchronize, reopened, labeled, unlabeled]
+  push:
+    tags: [ 'v[0-9]+.[0-9]+.[0-9]+*' ]
+jobs:
+  publish:
+    uses: dart-lang/ecosystem/.github/workflows/publish.yaml@main