Refactor action to use composite run steps and support cross-repository issue creation

- Changed action execution from Docker to composite with Python setup.
- Added `TARGET_REPO` input to allow issue creation in a specified repository.
- Updated `GitHubClient` to use `TARGET_REPO` for issue and milestone URLs.
- Enhanced README with instructions for cross-repository usage.
- Introduced example workflow for creating TODO issues in another repository.

Signed-off-by: Shakar Bakr <5h4k4r.b4kr@gmail.com>

.github/workflows/example-cross-repo.yml

@@ -0,0 +1,34 @@
+name: Create TODO Issues in Another Repository
+
+# NOTE: This is an example for when the TARGET_REPO feature is released.
+# The current published version of the action does not yet have this feature.
+
+on:
+  push:
+    branches: [main, master]
+
+permissions:
+  contents: read
+  issues: write
+
+jobs:
+  todo-to-issue:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 0 # Required to get the diff between commits
+
+      - name: TODO to Issue
+        # Use the local version of the action (after you've made the changes)
+        uses: ./
+        with:
+          TARGET_REPO: "my-org/target-repo" # Replace with your target repository
+          TOKEN: ${{ secrets.CROSS_REPO_TOKEN }} # Token with access to the target repository
+          CLOSE_ISSUES: "true" # Optional: close issues when TODOs are removed
+          AUTO_ASSIGN: "true" # Optional: assign issues to the committer
+
+
+          # Other optional configurations:
+          # IDENTIFIERS: '{"TODO": "TODO:", "FIXME": "Fix needed:"}'  # Custom identifiers for TODOs
+          # LABELS: 'todo,fixme'  # Default labels to apply to all created issues