Add max_jobs config parity to the Slack sink

[YuyangXueEd]

Summary

The serverchan sink already supports max_jobs, but the Slack sink still hardcodes the jobs section to 3 items.

This is a nice scoped parity fix for a new contributor.

Suggested changes

• Update sinks/slack/__init__.py so SlackSink reads max_jobs from sinks.slack.max_jobs
• Keep the default at 3
• Update sinks/slack/README.md config examples and option table
• Add or update tests to cover the jobs limit behavior

Acceptance criteria

• sinks.slack.max_jobs is respected when jobs are present in the payload
• Default behavior stays the same when max_jobs is omitted
• README documents the new option
• Relevant tests pass

Pointers

• sinks/slack/__init__.py
• sinks/slack/README.md
• tests/ (a new tests/test_slack_sink.py would be a reasonable place)

[Maharshi-Project]

Interesting, I’ll take the lead on it. I’ll keep you posted on my progress and reach out if I hit any roadblocks before submitting a PR.