Merge throughput tool docs into one page (#6956)

* Merge transport articles into index

* Merge FAQ and determine message transport

* Titles and warning

* Update nservicebus/throughput-tool/index.md

Co-authored-by: Mike Minutillo <[email protected]>

---------

Co-authored-by: Mike Minutillo <[email protected]>

Author: DavidBoike

menu/menu.yaml

@@ -778,6 +778,8 @@
       Title: Overview
     - Url: nservicebus/tools/migrate-to-native-delivery
       Title: Migrating timeouts
+    - Url: nservicebus/throughput-tool
+      Title: Measuring usage using legacy tool
   - Title: Troubleshooting
     Articles:
     - Url: nservicebus/troubleshooting/message-loss