Add pipeline for pushing to pub.dev on tag creation (#164)

* workflows: Add workflow for publishing on tag creation

* Update .github/workflows/publish.yml

---------

Co-authored-by: Foti Dim <foti@navideck.com>

Author: cadivus

.github/workflows/publish.yml

@@ -0,0 +1,38 @@
+name: Publish to pub.dev
+
+on:
+  push:
+    tags:
+    # must align with the tag-pattern configured on pub.dev, often just replace
+    #  with [0-9]+.[0-9]+.[0-9]+*
+    - '[0-9]+.[0-9]+.[0-9]+*' # tag-pattern on pub.dev: ''
+    # If you prefer tags like '1.2.3', without the 'v' prefix, then use:
+    # - '[0-9]+.[0-9]+.[0-9]+*' # tag-pattern on pub.dev: ''
+    # If your repository contains multiple packages consider a pattern like:
+    # - 'my_package_name-v[0-9]+.[0-9]+.[0-9]+*'
+
+# Publish using the reusable workflow from dart-lang.
+jobs:
+  publish:
+    permissions:
+      id-token: write # Required for authentication using OIDC
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Get flutter version
+        run: echo "flutter_version=`cat .flutter_version`" >> $GITHUB_ENV
+        id: flutter_version
+      - uses: subosito/flutter-action@v2
+        with:
+          channel: "stable"
+          cache: true
+          flutter-version: ${{ env.flutter_version }}
+      - run: flutter pub get
+      - name: Create publishing token (flutter)
+        run: |
+          set -eo pipefail
+          PUB_TOKEN=$(curl --retry 5 --retry-connrefused -sLS "${ACTIONS_ID_TOKEN_REQUEST_URL}&audience=https://pub.dev" -H "User-Agent: actions/oidc-client" -H "Authorization: Bearer $ACTIONS_ID_TOKEN_REQUEST_TOKEN" | jq -r '.value')
+          echo "PUB_TOKEN=${PUB_TOKEN}" >> $GITHUB_ENV
+          export PUB_TOKEN
+          flutter pub token add https://pub.dev --env-var PUB_TOKEN
+      - run: flutter pub publish --force # --force because of the web dependency