WEB3-49: Add workflow to find or create Linear issue from PR (#182)

Simmilar to in other repos, this PR adds a GitHub Actions workflow to
find or create a Linear issue when a PR is created

I managed to find the UUID for the "In Progress" state on the Web3 team
using the following API query:

```sh
curl \-X POST \
  -H "Content-Type: application/json" \
  -H "Authorization: ${LINEAR_API_KEY:?}" \
  --data '{ "query": "{ workflowStates { nodes { id name type team { name } } } }" }' \
  https://api.linear.app/graphql | jq
```

---------

Co-authored-by: Wolfgang Welz <[email protected]>

.github/workflows/linear.yml

@@ -0,0 +1,28 @@
+name: Find or Create Linear Issue for PR
+
+on:
+  workflow_dispatch:
+  pull_request:
+    branches:
+      - main
+    types: ["opened", "edited", "reopened", "synchronize"]
+
+permissions:
+  pull-requests: write
+  repository-projects: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: false
+
+jobs:
+  create-linear-issue-pr:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Find or create a Linear Issue
+        uses: risc0/action-find-or-create-linear-issue@risc0
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          linear-api-key: ${{ secrets.LINEAR_API_KEY }}
+          linear-team-key: "WEB3"
+          linear-created-issue-state-id: "2505ebd6-1fbe-4b25-b2a8-792dfaa50ad9" # in progress