Improvise the slack Alerts for downtime/resolve Alerts

**Is your feature request related to a problem? Please describe.**
I would like to have slack notification message more compact similar to what uptimeRobot does.

**Describe the solution you'd like**

the Down Alert and UpAlert should give clarity about the Root cause, length of downtime, The URL checked. I am attaching the screenshot of uptimeRobot Alerts

**Describe alternatives you've considered**
UptimeRobot alerts

Look for Slack notification code, likely in a notification handler or alerting module. The issue wants more compact messages with root cause, downtime length, and URL. Start by finding where Slack alerts are formatted and sent, then modify to include the requested details. Check existing tests for notifications to ensure changes work.

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