docs: replace pkg-config with pkgconf in Formula Cookbook and tests

[chenrui333]

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This aligns with what we are doing in homebrew-core.

[Copilot]

Pull Request Overview

This PR updates documentation and test examples to reflect the replacement of pkg-config with pkgconf as the preferred package configuration tool in Homebrew formulas.

• Updated Formula Cookbook documentation to use pkgconf instead of pkg-config in examples
• Updated RuboCop test fixtures to use pkgconf for consistency
• Modified naming guidelines to reference pkgconf as the canonical example

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
docs/Formula-Cookbook.md	Updated three example code blocks and naming guidelines to reference pkgconf instead of pkg-config
Library/Homebrew/test/rubocops/components_order_spec.rb	Updated test fixture examples to use pkgconf for consistency with updated documentation

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