feat: esbuild 0.21.x (#1272)

Upgrades esbuild to ^0.21.0.

Please not that according to the support policy, minor version upgrades of esbuild might include breaking changes. See the esbuild release for details: https://github.com/evanw/esbuild/releases/tag/v0.21.0

That said, for this release the esbuild release notes explicitly state "This release doesn't contain any deliberately-breaking changes.".

To stay on a different version of esbuild, see https://github.com/mrgrain/cdk-esbuild?tab=readme-ov-file#tsjs-how-can-i-use-a-different-version-of-esbuild