Add AllowedPredicates configuration option to Rails/Env

[dduugg]

Summary

Replace Rails/Env's hard-coded ALLOWED_LIST constant with a configurable AllowedPredicates option. The default value is the previous ALLOWED_LIST content — String / StringInquirer predicates like empty?, match?, between? — so out-of-the-box behavior is unchanged.

The motivation is to let users exempt additional predicates from the cop without forking or disabling it. Two concrete cases this addresses:

• Rails.env.local? — the built-in alias for "development or test", introduced in Rails 7.1. Some users treat it as a legitimate guard rail for code that should only ever execute in dev or test (sanity checks, devtools, seed data) rather than as an environment-rollout mechanism, and want it exempt from the cop.
• Custom predicates monkey-patched onto the environment inquirer. Apps with their own Rails.env.beta_user? / Rails.env.internal? style helpers can now opt those in.

The configured value fully replaces the default — it is not merged. Users who want to inherit the defaults and add to them can opt in via RuboCop's inherit_mode:

Rails/Env:
  AllowedPredicates:
    - empty?
    - match?
    - local?

Compatibility with Rails/EnvLocal

Rails/EnvLocal autocorrects Rails.env.development? || Rails.env.test? → Rails.env.local?. Under the default AllowedPredicates, Rails/Env will still flag the autocorrected Rails.env.local?. Users who run both cops can now resolve that conflict by including local? in their AllowedPredicates rather than disabling either cop.

Test coverage

A new context block uses let(:cop_config) to override AllowedPredicates and verifies (a) a predicate in the override is not flagged, and (b) a predicate omitted from the override is flagged — confirming the override is exhaustive (no implicit merge with defaults).

Before submitting the PR make sure the following are checked:

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (no related issue).
• Feature branch is up-to-date with master.
• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default.
• Added an entry to the changelog folder.
• If this is a new cop, consider making a corresponding update to the Rails Style Guide (N/A — existing cop).

[corsonknowles]

Great fix! Thanks for the added versatility.

And we need this now as well, because we do allow .local?