Migrations:
* add a new column alert_group_idx to alert_rule table
* add a new column alert_group_idx to alert_rule_version table
* re-index existing rules during migration
API:
* set group index on update. Use the natural order of items in the array as group index
* sort rules in the group on GET
* update the version of all rules of all affected groups. This will make optimistic lock work in the case of multiple concurrent request touching the same groups.
UI:
* update UI to keep the order of alerts in a group
* Alerting: Expose discovered and dropped Alertmanagers
Exposes the API for discovered and dropped Alertmanagers.
* make admin config poll interval configurable
* update after rebase
* wordsmith
* More wordsmithing
* change name of the config
* settings package too
