* add VersionedNotifierPlugin and method that converts NotifierPlugin to it
* return new schema if query parameter version=2
* add version to k8s model of integration
* fix open api snapshot
* add version to IntegrationConfig
* use current version on conversion
* create versioned integrations for test
* Alerting: Add CustomDetails for PagerDuty
* fix default value for 'severity' from 'error' to 'critical'
* minimal docs for notifiers, specifying config for PagerDuty
* replace notifier -> integration
* replace notifier -> integration