Remove --preview as a required argument for ruff server

[snowsignal]

Summary

ruff server has reached a point of stabilization, and --preview is no longer required as a flag.

--preview is still supported as a flag, since future features may be need to gated behind it initially.

Test Plan

A simple way to test this is to run ruff server from the command line. No error about a missing --preview argument should be reported.

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

ℹ️ ecosystem check encountered linter errors. (no lint changes; 1 project error)

demisto/content (error)

ruff check --no-cache --exit-zero --ignore RUF9 --output-format concise --preview

warning: The top-level linter settings are deprecated in favour of their counterparts in the `lint` section. Please update the following options in `pyproject.toml`:
  - 'ignore' -> 'lint.ignore'
  - 'select' -> 'lint.select'
  - 'unfixable' -> 'lint.unfixable'
  - 'per-file-ignores' -> 'lint.per-file-ignores'
warning: `PGH001` has been remapped to `S307`.
warning: `PGH002` has been remapped to `G010`.
warning: `PLR1701` has been remapped to `SIM101`.
ruff failed
  Cause: Selection of deprecated rule `E999` is not allowed when preview is enabled.

[MichaReiser]

I'm okay merging this but there are at least two follow-ups that are necessary

• Don't set the --preview flag in ruff-vscode if the server version is >= 0.5. We should do this pre-release to avoid that users will unintentionally opt in the future.
• I would expect that ruff server --preview works the same as ruff check --preview and ruff format --preview and enables all --preview features (linter and formatter).

I would expect that running ruff server --preview would enable all preview features similar to setting preview = true in the settings.

[snowsignal]

@MichaReiser Thanks for the review! I'll look into addressing the points you brought up.

I would expect that running ruff server --preview would enable all preview features similar to setting preview = true in the settings.

We also have server settings, lint.preview, and format.preview, that control this behavior. We should make it clear that this would override those settings.