chore: add PR title linter (#181)

- Basic workflow to lint the PR title to enforce conventional commit
titles
- Copied from lodestar repo
- Resolves #172

Author: wemeetagain

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

@@ -0,0 +1,69 @@
+name: "Lint PR title"
+
+on:
+  pull_request_target:
+    types:
+      - opened
+      - edited
+      - synchronize
+      - labeled
+      - unlabeled
+
+jobs:
+  main:
+    name: Validate PR title
+    runs-on: ubuntu-latest
+    steps:
+      - uses: amannn/action-semantic-pull-request@v5
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          # Configure which types are allowed (newline-delimited).
+          # Default: https://github.com/commitizen/conventional-commit-types
+          # Customized based on sections defined in scripts/generate_changelog.mjs
+          types: |
+            feat
+            fix
+            perf
+            refactor
+            revert
+            deps
+            build
+            ci
+            test
+            style
+            chore
+            docs
+
+          # Configure which scopes are allowed (newline-delimited).
+          # These are regex patterns auto-wrapped in `^ $`.
+          #scopes: |
+
+          # Configure that a scope must always be provided.
+          requireScope: false
+
+          # Configure which scopes are disallowed in PR titles (newline-delimited).
+          # For instance by setting the value below, `chore(release): ...` (lowercase)
+          # and `ci(e2e,release): ...` (unknown scope) will be rejected.
+          # These are regex patterns auto-wrapped in `^ $`.
+          #disallowScopes: |
+
+          # Configure additional validation for the subject based on a regex.
+          # This example ensures the subject doesn't start with an uppercase character.
+          subjectPattern: ^(?![A-Z]).+$
+
+          # If `subjectPattern` is configured, you can use this property to override
+          # the default error message that is shown when the pattern doesn't match.
+          # The variables `subject` and `title` can be used within the message.
+          subjectPatternError: |
+            The subject "{subject}" found in the pull request title "{title}"
+            didn't match the configured pattern. Please ensure that the subject
+            doesn't start with an uppercase character.
+
+          # If the PR contains one of these newline-delimited labels, the
+          # validation is skipped. If you want to rerun the validation when
+          # labels change, you might want to use the `labeled` and `unlabeled`
+          # event triggers in your workflow.
+          ignoreLabels: |
+            bot
+            ignore-semantic-pull-request