feat(health): add new Redis alarms (#13715)

health/health.d/redis.conf

@@ -1,3 +1,18 @@
+# you can disable an alarm notification by setting the 'to' line to: silent
+
+ template: redis_connections_rejected
+ families: *
+       on: redis.connections
+    class: Errors
+     type: KV Storage
+component: Redis
+   lookup: sum -1m unaligned of rejected
+    every: 10s
+    units: connections
+     warn: $this > 0
+     info: connections rejected because of maxclients limit in the last minute
+    delay: down 5m multiplier 1.5 max 1h
+       to: dba
 
  template: redis_bgsave_broken
  families: *
@@ -26,3 +41,17 @@ component: Redis
      info: duration of the on-going RDB save operation
     delay: down 5m multiplier 1.5 max 1h
        to: dba
+
+ template: redis_master_link_down
+ families: *
+       on: redis.master_link_down_since_time
+    class: Errors
+     type: KV Storage
+component: Redis
+    every: 10s
+     calc: $time
+    units: seconds
+     crit: $this != nan AND $this > 0
+     info: time elapsed since the link between master and slave is down
+    delay: down 5m multiplier 1.5 max 1h
+       to: dba