Chore: Add issue/PR template, CoC and Contributing guide (#774)

- Added issue and PR templates
- Improved issue chooser
- Added Code of Conduct and Contributing guide
  - Includes contributor agreement to Apache 2.0

.github/pull_request_template.md

@@ -0,0 +1,23 @@
+### Description
+<!-- Describe your changes in detail. What problem does this PR solve? -->
+
+### Type of Change
+<!-- Put an 'x' in all boxes that apply -->
+
+- [ ] 🐛 Bug fix (non-breaking change which fixes an issue)
+- [ ] ✨ New feature (non-breaking change which adds functionality)
+- [ ] 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
+- [ ] 📚 Documentation update
+
+### Pre-flight Checklist
+<!-- Put an 'x' in all boxes that apply -->
+
+- [ ] Changes are limited to a single feature, bugfix or chore (split larger changes into seperate PRs)
+- [ ] Tests are passing (`npm test`) and code is formatted and linted (`npm run format && npm run lint`)
+- [ ] I have reviewed [contributor guidelines](https://github.com/cline/cline/blob/main/CONTRIBUTOR.md)
+
+### Screenshots
+<!-- For UI changes, add screenshots here -->
+
+### Additional Notes
+<!-- Add any additional notes for reviewers -->