Dylan/request throttle (#10413)

* request throttling -- initial implementation

* prevented semaphore leak; added xml docs

* small doc fixes

* reference document

* Added internals folder, added structured logging,

* removed typo'd dependency

* no default MaxConcurrentRequests; other polishing

* renamed SemaphoreWrapper->RequestQueue; cleanup

* moved SyncPoint; prevented possible semaphore leak

* adjusting feedback

* regen refs

* Final changes!