[Reviewer: Ellie] Log relevant statistics to SAS when overloaded

https://github.com/Metaswitch/clearwater-sas-resources/commit/6f273fb78d01f36ac82e29e7dd9fa6bcf5b6285e is the SAS bundle change. https://github.com/Metaswitch/cpp-common/pull/165 makes a similar change to HTTP requests.