Improve the codegen diff bot (#918)

.github/workflows/codegen-preview.yml

tools/ci-cdk/.eslintrc.json

tools/ci-cdk/.gitignore

tools/ci-cdk/.npmignore

tools/ci-cdk/.prettierrc

tools/ci-cdk/LICENSE

tools/ci-cdk/README.md

tools/ci-cdk/bin/ci-cdk.ts

tools/ci-cdk/cdk.json

tools/ci-cdk/jest.config.js

tools/ci-cdk/lib/constructs/cloudfront-s3-cdn.ts

tools/ci-cdk/lib/constructs/github-oidc-role.ts

tools/ci-cdk/lib/smithy-rs/pull-request-cdn-stack.ts

tools/ci-cdk/package-lock.json

tools/ci-cdk/package.json

tools/ci-cdk/test/constructs/github-oidc-role.test.ts

tools/ci-cdk/tsconfig.json

tools/codegen-diff-revisions.py

tools/mk-generated.sh