live: experimental HA with Redis (#36787)

Grafana 8.1.0 will include experimental high availability setup support by
using Redis PUB/SUB and data structures for inter-node state sharing.
This commit documents this but also explicitly marks feature as experimental
since integration of Live with Redis may slightly evolve with time as soon as
we get more understanding about Grafana Live usage scenarios.

docs/sources/administration/configuration.md

@@ -1529,6 +1529,30 @@ For example:
 allowed_origins = "https://*.example.com"
 ```
 
+### ha_engine
+
+> **Note**: Available in Grafana v8.1 and later versions.
+
+**Experimental**
+
+The high availability (HA) engine name for Grafana Live. By default, it's not set. The only possible value is "redis".
+
+For more information, refer to [Configure Grafana Live HA setup]({{< relref "../live/live-ha-setup.md" >}}).
+
+### ha_engine_address
+
+> **Note**: Available in Grafana v8.1 and later versions.
+
+**Experimental**
+
+Address string of selected the high availability (HA) Live engine. For Redis, it's a `host:port` string. Example:
+
+```ini
+[live]
+ha_engine = redis
+ha_engine_address = 127.0.0.1:6379
+```
+
 <hr>
 
 ## [plugin.grafana-image-renderer]