Change documentation of MB_SESSION_TIMEOUT to be JSON format (#29186)

* change documentation

* change code comment to match

docs/configuring-metabase/environment-variables.md

@@ -1206,7 +1206,7 @@ Since: v44.0
 
 Time before inactive users are logged out. By default, sessions last according to [MAX_SESSION_AGE](#max_session_age) and [MB_SESSION_COOKIES](#mb_session_cookies).
 
-Has to be in the format `"{:amount 60 :unit 'minutes'}"` where the unit is one of "seconds", "minutes" or "hours".
+Has to be in the JSON format `"{\"amount\":120,\"unit\":\"minutes\"}"` where the unit is one of "seconds", "minutes" or "hours".
 
 ### `MB_SETUP_TOKEN`
 

src/metabase/server/middleware/session.clj

@@ -373,7 +373,7 @@
         :amount-must-be-less-than-100-years))))
 
 (defsetting session-timeout
-  ;; Should be in the form {:amount 60 :unit "minutes"} where the unit is one of "seconds", "minutes" or "hours".
+  ;; Should be in the form "{\"amount\":60,\"unit\":\"minutes\"}" where the unit is one of "seconds", "minutes" or "hours".
   ;; The amount is nillable.
   (deferred-tru "Time before inactive users are logged out. By default, sessions last indefinitely.")
   :type    :json