Add attribution handling to the layer

[fityannugroho]

Summary

This PR introduces enhancements to improve attribution handling. The key changes include dynamic retrieval of attributions from MapLibre styles, support for custom attribution controls, and additional events to synchronize attribution updates.

Key Changes

Custom Attribution Handling

• Feature: The getAttribution method now dynamically retrieves attributions from MapLibre style sources if attributionControl is enabled and no custom attribution is specified.
• Fallback: If no valid attributions are found, it defaults to an empty string.

Automatic Attribution Update on Map Load

• Added an event listener to the load event of the MapLibre instance to update the Leaflet map's attribution control dynamically after the MapLibre map has fully loaded.

Why This Change?

• Dynamic Attribution Support: Automatically gathering attributions from MapLibre sources ensures compliance with licensing terms without requiring manual input.
• Customization Flexibility: Developers can specify their own attributions via options.attributionControl.customAttribution when needed.