.NET: Workflow getting started samples in .Net (Second batch) (#650)
* Add loop and agents in workflows samples
* Add foundry agent and workflow as agent samples
* Checkpoint sample WIP
* Checkpoint sample 1 Done
* Add HIL samples
* Fix formatting
* Force folder name change step 1
* Force folder name change step 2
* Fix formatting
* Fix formatting
* Add checkpoint and rehydrate sample
* _Foundational
* Fix formatting
Tao Chen