Add more documentation

Signed-off-by: ishitasequeira <ishiseq29@gmail.com>

controller/sharding/sharding_test.go

@@ -672,9 +672,6 @@ func Test_getOrUpdateShardNumberForController(t *testing.T) {
 			heartbeatCurrentTime = func() metav1.Time { return expectedTime }
 			shard, shardMappingData := getOrUpdateShardNumberForController(tc.shardApplicationControllerMapping, tc.hostname, tc.replicas, tc.shard)
 			assert.Equal(t, tc.expectedShard, shard)
-			// for i, shardMapping := range shardMappingData {
-			// 	assert.True(t, tc.expectedShardMappingData[i].Equals(&shardMapping))
-			// }
 			assert.Equal(t, tc.expectedShardMappingData, shardMappingData)
 		})
 	}

docs/operator-manual/high_availability.md

@@ -78,6 +78,22 @@ spec:
       - name: argocd-application-controller
 ```
 
+* The application controller will use the configMap `argocd-app-controller-shard-cm` to store the controller to shard mapping and the heartbeat. The ConfigMap would look like:
+
+```yaml
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: my-configmap
+data:
+  shardControllerMapping:
+    - ControllerName: "example-controller"
+      ShardNumber: 0
+      Heartbeat: Wed Sep 20 08:05:26
+```
+
+The heartbeat of the controller will be updated during every cheack of readiness probe (that is every 10 seconds). 
+
 * The shard distribution algorithm of the `argocd-application-controller` can be set by using the `--sharding-method` parameter. Supported sharding methods are : [legacy (default), round-robin]. `legacy` mode uses an `uid` based distribution (non-uniform). `round-robin` uses an equal distribution across all shards. The `--sharding-method` parameter can also be overriden by setting the key `controller.sharding.algorithm` in the `argocd-cmd-params-cm` `configMap` (preferably) or by setting the `ARGOCD_CONTROLLER_SHARDING_ALGORITHM` environment variable and by specifiying the same possible values.
 
 !!! warning "Alpha Feature"