feat(logs): add alloy + loki

[0xNineteen]

• mac support
• linux support

note: alerting requires proper parsing of logs which requires some changes to our logger which ill put into a separate PR

• logs are stored in logs/sig.log
• alloy scrapes the logs and pushes to loki
• loki is a log database which we query from grafana on the explore page (dashboards + alerting coming in future PR -- see note)

TL;DR

Added log aggregation capabilities to the metrics stack using Loki and Alloy.

What changed?

• Added Loki for log storage and querying
• Added Alloy for log collection and forwarding
• Updated Grafana configuration to include Loki as a data source
• Added /logs to gitignore
• Consolidated message handle time metrics into the main Gossip dashboard
• Updated documentation for running with logs

How to test?

1. Run sig with log output: ./zig-out/bin/sig gossip -n testnet 2>&1 | tee -a logs/sig.log
2. Start the metrics stack:
   • Mac: docker compose -f compose_mac.yaml up -d
   • Linux: docker compose -f compose_linux.yaml up -d
3. Access Grafana at localhost:3000 and verify logs are visible in Explore view
4. Verify metrics dashboards show handle time data correctly

[0xNineteen]

• feat(logs): logfmt standard + provisioned slack alerts #475
• feat(logs): add alloy + loki #451 👈 (View in Graphite)
• main

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[Sobeston]

Had a few hitches getting things up, but seems generally good.

[0xNineteen]

cc: @dnut i think https://github.com/orgs/Syndica/projects/2/views/16?pane=issue&itemId=92360295 is solved here

[dnut]

Looks good, but I just had a few minor nitpicks. I'm not very opinionated about any of this, so feel free to turn them down.

[Sobeston]