Add ability to sync .gitignore files across repositories with repo-specific preservation

[Copilot]

Overview

This PR adds the ability to sync .gitignore files across multiple repositories via pull requests, similar to how dependabot.yml syncing works. This addresses the feature request in #[issue_number] to sync gitignore files while allowing repository-specific variances.

Key Features

1. New Input Parameters

• gitignore: Path to a .gitignore file to sync to target repositories
• gitignore-pr-title: Title for pull requests when updating .gitignore (default: chore: update .gitignore)

2. Repository-Specific Content Preservation

The implementation includes a unique feature to preserve repository-specific entries at the end of .gitignore files. Content after a # Repository-specific entries (preserved during sync) marker is kept intact during syncs, allowing you to maintain bulk consistency while supporting repo-specific exceptions.

Example:

# Standard entries (synced from source)
node_modules/
dist/
*.log

# Repository-specific entries (preserved during sync)
scanresults.json
twistlock-*.md

When syncing, the standard entries are updated from the source file while scanresults.json and twistlock-*.md remain untouched in the target repository.

3. Usage Examples

Basic usage:

- name: Sync .gitignore
  uses: joshjohanning/bulk-github-repo-settings-sync-action@v1
  with:
    github-token: ${{ steps.app-token.outputs.token }}
    repositories-file: 'repos.yml'
    gitignore: './config/gitignore/.gitignore'
    gitignore-pr-title: 'chore: update .gitignore'

Per-repository overrides:

repos:
  - repo: owner/repo1
    gitignore: './config/gitignore/node.gitignore'
  - repo: owner/repo2
    gitignore: './config/gitignore/python.gitignore'
  - repo: owner/repo3
    gitignore: './.gitignore' # use this repo's .gitignore

Implementation Details

• syncGitignore function: Mirrors the syncDependabotYml implementation pattern for consistency
• Smart content merging: Automatically detects and preserves repo-specific content
• PR management: Creates new PRs or detects existing ones to avoid duplicates
• Verified commits: Uses GitHub API for commit creation, ensuring verified status
• Dry-run support: Preview changes without applying them
• Comprehensive error handling: Gracefully handles missing files, API errors, and permission issues

Testing

Added 9 new test cases covering:

• Creating .gitignore when it doesn't exist
• Updating .gitignore when content differs
• Preserving repository-specific content
• Skipping when content is unchanged
• Detecting existing PRs
• Dry-run mode
• Error scenarios (invalid format, missing file, API errors)

All 51 tests pass ✅

Documentation

• Updated README with usage examples and behavior documentation
• Added to features list
• Updated authentication requirements (requires Contents and Pull Requests permissions)
• Included example .gitignore file and YAML configuration

Version

Bumped version from 1.1.1 to 1.2.0 (minor version bump for new feature)

Related Issues

Fixes #[issue_number]

Warning

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  • Triggering command: node /home/REDACTED/work/bulk-github-repo-settings-sync-action/bulk-github-repo-settings-sync-action/node_modules/.bin/make-coverage-badge-better --label-color #333 --output-path ./badges/coverage.svg (dns block)

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Original prompt

---

This section details on the original issue you should resolve

<issue_title>Add ability to sync gitignore</issue_title>
<issue_description>Sync gitignore by repo just like dependabot</issue_description>

Comments on the Issue (you are @copilot in this section)

@joshjohanning Require the bulk to be the same but allow for some variances at the end, like this with the twistlock config

</comment_new>

Fixes #14

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