docs: remove uptimerobot references and add note about monitoring

[shreddedbacon]

General Checklist

• Affected Issues have been mentioned in the Closing issues section
• Documentation has been written/updated
• PR title is ready for inclusion in changelog

Database Migrations

• If your PR contains a database migation, it MUST be the latest in date order alphabetically

Removes references to UptimeRobot and updates documentation for the monitoring-path on routes to include a note that Lagoon does not provide monitoring capabilties out of the box, and that only labels and annotations are provided.

It is up to platform operators to use these labels and annotations to inform monitoring systems as they see fit.

As always though, people are free to add their own monitoring that they manage themselves outside of Lagoon if a platform operator does not offer a monitoring solution.

[tobybellwood]

Thanks!