docs(alerting): new best practices guide (#115687)
* Split best practices section
* Write Examples and Guides docs
* Move recording rule recommendations
* docs(alerting): new best practices guide
* fix vale errors
* Detail meaning of alert `escalation`
* Include the recovery threshold option
* Include lower severity channels for infrastructure alerts
* Remove timing options
* minor intro edits
* Rename heading to avoid gerunds
(cherry picked from commit 0bfcc55411)
Pepe Cano