fix(mercure): use precise wording when describing routes

The term `APP_NAME` was misleading cause previously it refers to mercure
with `SERVICE_NAME`.

Author: danmilon

sites/platform/src/add-services/mercure.md

@@ -88,12 +88,12 @@ Note that changing the name of the service replaces it with a brand new service
 
 ### 2. Define the route
 
-Include an entry in your `.platform/routes.yaml` file as shown below, replacing <APP_NAME> with the name of your Mercure app:
+Include an entry in your `.platform/routes.yaml` file as shown below, replacing <SERVICE_NAME> with the name of your Mercure service:
 
 ```yaml {configFile="routes"}
 "https://mercure.{default}/":
    type: upstream
-   upstream: "<APP_NAME>:mercure"
+   upstream: "<SERVICE_NAME>:mercure"
 ```
 
 ### 3. Define the relationship 
@@ -174,7 +174,7 @@ mercure:
 ```yaml {configFile="routes"}
 "https://mercure.{default}/":
    type: upstream
-   upstream: "<APP_NAME>:mercure"
+   upstream: "<SERVICE_NAME>:mercure"
 ```
 
 #### [App configuration](/create-apps/_index.md)

sites/upsun/src/add-services/mercure.md

@@ -143,13 +143,13 @@ Note that changing the name of the service replaces it with a brand new service
 
 ### 2. Define the route
 
-To access the service URL, add an entry to the `.routes` key as shown below, replacing <APP_NAME> with the name of your app: 
+To access the service URL, add an entry to the `.routes` key as shown below, replacing <SERVICE_NAME> with the name of your service: 
 
 ```yaml {configFile="app"}
 routes: 
   "https://mercure.{default}/":
     type: upstream
-    upstream: "<APP_NAME>:mercure"
+    upstream: "<SERVICE_NAME>:mercure"
 ```
 
 ### 3. Define the relationship