feat: Deal with large repos via lightweight mode

[renan-alm]

This pull request introduces a new "lightweight sync" mode optimized for large repositories, along with supporting documentation, configuration, and implementation updates. The lightweight sync mode uses force push operations to speed up synchronization, especially for initial mirroring or periodic backups, and is now selectable via workflow inputs.

Lightweight Sync Mode Feature:

• Added use_lightweight_sync input to action.yml and documented it in README.md, allowing users to enable lightweight sync for large repositories. [1] [2]
• Provided detailed documentation in README.md explaining the benefits, use cases, and example configurations for lightweight sync mode.

Implementation:

• Created new module src/lightweight-sync.js implementing syncBranchesLightweight and syncTagsLightweight functions for fast, force-push-based branch and tag synchronization.
• Updated src/index.js to import the new lightweight sync functions and select the sync strategy based on the use_lightweight_sync input. [1] [2]
• Modified input parsing in src/index.js to support the new use_lightweight_sync option.