feat: enable turbopack in CI, fix various turbopack-related bugs

[AlessioGr]

This adds a new tests-e2e-turbo CI step that runs our e2e test suite against turbo. This will ensure that we can guarantee full support for turbopack.

Our CI runners are already at capacity, so the turbo steps will only run if the tests-e2e-turbo label is set on the PR.

Changes to improve turbopack compatibility

• Use correct sideEffects configuration to fix scss issues
• Import scss directly instead of duplicating our scss rules
• Fix some scss rules that are not supported by turbopack
• Bump Next.js and all other dependencies used to build payload

Changes to get tests to pass

For an unknown reason, flaky tests flake a lot more often in turbopack. This PR does the following to get them to pass:

• add more waits
• fix actual flakes by ensuring previous operations are properly awaited
• use new useQueue hook for relationship react-select field for loading options

Blocking turbopack bugs

• [X] https://github.com/vercel/next.js/issues/76464
  • Fix PR: https://github.com/vercel/next.js/pull/76545
  • Once fixed: change "sideEffectsDisabled": back to "sideEffects":

Non-blocking turbopack bugs

• [ ] https://github.com/vercel/next.js/issues/76956