[MM-557] Added workflow file to add new issues to github board (#387)

.github/workflows/issue_add.yml

@@ -0,0 +1,26 @@
+name: issue_add
+
+on:
+  issues:
+    types:
+      - opened
+
+permissions:
+  repository-projects: write
+
+jobs:
+  add-to-project:
+    if: ${{ github.repository_owner == 'mattermost' }}
+    name: Add issue to project
+    runs-on: ubuntu-latest
+    steps:
+      - uses: mattermost/github-app-installation-token-action@181cd1b8c94b158428c4facfe043d6e28c20be55
+        id: ghapp
+        with:
+          appId: "${{ vars.UNIFIED_CI_APP_ID }}"
+          installationId: "${{ vars.UNIFIED_CI_INSTALLATION_ID }}"
+          privateKey: ${{ secrets.UNIFIED_CI_PRIVATE_KEY }}
+      - uses: actions/add-to-project@31b3f3ccdc584546fc445612dec3f38ff5edb41c #v0.5.0
+        with:
+          project-url: https://github.com/orgs/mattermost/projects/9
+          github-token: ${{ steps.ghapp.outputs.token }}