chore: add flow for triaging external PRs

.github/workflows/autoassign-prs.yml

@@ -0,0 +1,36 @@
+name: PR autoassignment
+
+on:
+  pull_request:
+    types: [opened]
+
+jobs:
+  assign-new-issue:
+    runs-on: ubuntu-latest
+    permissions:
+      pull-requests: write
+    steps:
+      - uses: actions/github-script@v6
+        with:
+          script: |
+            const externalPrTriager = "kanej";
+
+            // Within the Github API PRs are issue objects
+            const pr = await github.rest.issues.get({
+              owner: context.issue.owner,
+              repo: context.issue.repo,
+              issue_number: context.issue.number
+            });
+
+            const isCollaborator = ["OWNER", "MEMBER", "COLLABORATOR"].includes(pr.data.author_association)
+
+            if (isCollaborator) {
+              return
+            }
+
+            await github.rest.issues.addAssignees({
+              owner: context.issue.owner,
+              repo: context.issue.repo,
+              issue_number: context.issue.number,
+              assignees: [externalPrTriager],
+            });