Add configurable distribution modes for federation delivery

[pfefferle]

Summary

Add a setting to allow site administrators to choose how aggressively the plugin distributes activities to remote servers. This helps manage server load from HTTP signature verifications on both the sending server and receiving instances.

Proposed Modes

1. Default — Deliver activities as fast as possible (current behavior)
2. Balanced — Moderate pace with reasonable pauses between batches
3. Eco Mode 🌱 — Take your time, gentle on server resources
4. Custom — Configure batch size and delay manually

Technical Details

Each mode adjusts these parameters:

Parameter	Default	Balanced	Eco Mode	Custom
Batch size	100	50	20	User-defined
Pause between batches	30s	60s	300s (5min)	User-defined

Key filters involved:

• activitypub_dispatcher_batch_size
• activitypub_scheduler_async_batch_pause

Use Cases

• Shared hosting — Use "Eco Mode" to avoid hitting resource limits
• High-traffic sites — Use "Default" when server can handle the load
• Large follower counts — Use "Balanced" to spread load over time
• Fine-tuned setups — Use "Custom" for specific requirements

Settings Location

Add to ActivityPub settings page, possibly under "Advanced" or new "Performance" section.