scheduler: add scheduler period to framework_set_scheduler

Adds scheduler period in Parameters and Example sections of framework_set_scheduler.

Signed-off-by: Krzysztof Karas <krzysztof.karas@intel.com>
Change-Id: I05dbe20fb73aefe4dc8fa60f659f63d5a4d88db6
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/6043
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-by: Aleksey Marchuk <alexeymar@mellanox.com>
Reviewed-by: Maciej Szwed <maciej.szwed@intel.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>

doc/jsonrpc.md

@@ -697,6 +697,7 @@ This feature is considered as experimental.
 Name                    | Optional | Type        | Description
 ----------------------- | -------- | ----------- | -----------
 name                    | Required | string      | Name of a scheduler
+period                  | Optional | number      | Scheduler period
 
 ### Response
 
@@ -712,7 +713,8 @@ Example request:
   "method": "framework_set_scheduler",
   "id": 1,
   "params": {
-    "name": "static"
+    "name": "static",
+    "period": "1000000"
   }
 }
 ~~~