Load Balancing Plugin for Relayers

[zeljkoX]

Describe the feature

Create a new load balancing plugin that accepts incoming transactions and distributes them efficiently across multiple relayers.
The goal is to improve throughput, reliability, and resilience when handling transaction submissions to different relayers, while minimizing the need for users to implement their own balancing logic.

Technical Details:

• Expose a standardized interface for transaction submission (e.g., submit_transaction), abstracting relayer details from the user.
• Implement health-tracking logic based on:
• Response times and latency.
• Error and timeout rates.
• Availability status.
• Use a weighted or adaptive load balancing strategy that prioritizes healthy and performant relayers.