feat: add PR title linting workflow (#5)

* feat: add PR title linting workflow

* runs on slim

* feat: enforce lowercase start for PR title subjects

Author: HotThoughts

.github/workflows/lint-pr-title.yml

@@ -0,0 +1,23 @@
+name: "Lint PR Title"
+
+on:
+  pull_request:
+    types:
+      - opened
+      - edited
+      - synchronize
+
+jobs:
+  main:
+    name: Validate PR Title
+    runs-on: ubuntu-slim
+    steps:
+      - name: Semantic PR Title
+        uses: amannn/action-semantic-pull-request@v5
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          # Enforce that the subject starts with a lowercase letter.
+          subjectPattern: ^[a-z].*$
+          subjectPatternError: |
+            The subject "{subject}" must start with a lowercase letter.