Enhance caching in setup-node with automatic package manager detection

[priya-kinthali]

Description:
This PR improves the caching behaviour in setup-node by introducing enhanced logic for detecting and enabling caching based on the package manager field in package.json when the cache input is not explicitly set.

Key changes:

• Updated the caching behaviour to be enabled by default when a packageManager field is detected in the package.json file and no cache input is provided.
• Introduced a new input package-manager-cache to control this automatic caching behaviour. By default, package-manager-cache is set to true, enabling caching when a valid package manager field is detected. To disable this automatic caching, set package-manager-cache to false.
• Updated documentation to reflect the new default caching behaviour and the addition of the package-manager-cache input.

Related issue:
#686

Check list:

• Mark if documentation changes are required.
• Mark if tests were added or updated to cover the changes.

[Copilot]

Pull Request Overview

This PR enhances the caching functionality in setup-node by introducing automatic package manager detection from package.json fields when no explicit cache input is provided. The enhancement includes a new input parameter to control this behavior and updates documentation to reflect the new default caching approach.

• Implements automatic package manager detection from packageManager and devEngines.packageManager fields in package.json
• Adds package-manager-cache input parameter (default: true) to control automatic caching behavior
• Updates documentation and adds comprehensive test coverage for the new functionality

Reviewed Changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/main.ts	Implements core logic for package manager detection and automatic caching
action.yml	Adds new package-manager-cache input parameter definition
README.md	Updates documentation to describe new automatic caching behavior
tests/main.test.ts	Adds comprehensive test coverage for automatic caching scenarios
.github/workflows/e2e-cache.yml	Adds end-to-end test for package manager field detection
src/cache-save.ts	Minor formatting change (empty line addition)

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