[Internal] docs: Add address caches conceptual flow (#3534)

* Rough draft

* Some more changes

* Adding a new section

* Some more refinement

* Some changes 

Lets get the feedback

* Some MISC changes

docs/SdkDesign.md

@@ -17,6 +17,74 @@ flowchart LR
     TransportClient <--> Service[(Cosmos DB Service)]
 ```
 
+## Address caches conceptual model
+
+![image](https://user-images.githubusercontent.com/6880899/199167007-bcc054c3-ecb1-4469-ba7d-eae52362e9cd.png)
+
+
+- CollectionCache: Dictionary<CollectionName/Rid, CollectionProperties>
+- CollectionRoutingMap: Single collection PartitionKeyRanges map
+- PartitionKeyRangeCache: Dictionary<CollectionName/Rid, CollectionRoutingMap>
+- GlobalPartitionEndpointManager: Per partition override state. Every reqeust will flow throgh
+    -   Today GlobalEndpointManager is at region scope only and doesn't look at the partition
+    -   Ideal abstraction is to fold it into GlobalEndpointManager --> extra hash computation
+        - Posible to refactor direct code and flow HashedValue down stream (more contract work with direct package)
+- AddressResolver: It does use IAddressCache (Above diagram missing it)
+
+
+```mermaid
+flowchart LR
+    subgraph CDB_account
+        subgraph CDB_Account_Endpoint
+            CDB_EP[[CosmosDB-Account/Endpoint]]
+        end
+
+        subgraph CDB_Account_Region1
+            CDBR1_GW[[CosmosDB-Account/Gateway/Region1]]
+            CDBR1_BE[[CosmosDB-Account/Backend/Region1]]
+        end
+        subgraph CDB_Account_RegionN
+            CDBRN_GW[[CosmosDB-Account/Gateway/Region1]]
+            CDBRN_BE[[CosmosDB-Account/Backend/RegionN]]
+        end
+    end
+    subgraph AddressCaches
+        GAC1[<a href='https://github.com/Azure/azure-cosmos-dotnet-v3/blob/master/Microsoft.Azure.Cosmos/src/Routing/GatewayAddressCache.cs'>GatewayAddressCache/R1</a>]
+        GACN[<a href='https://github.com/Azure/azure-cosmos-dotnet-v3/blob/master/Microsoft.Azure.Cosmos/src/Routing/GatewayAddressCache.cs'>GatewayAddressCache/RN</a>]
+
+        GAC1 --> |NonBlockingAsyncCache| CDBR1_GW
+        GAC1 -.-> CDBR1_BE
+        GACN -->  |NonBlockingAsyncCache| CDBRN_GW
+        GACN -.-> CDBRN_BE
+    end
+```
+
+### Sequence of interaction
+
+```mermaid
+sequenceDiagram
+    GlobalAddressResolver->>GlobalEndpointManager: ResolveServiceEndpoint(DocumentServiceRequest)
+    GlobalEndpointManager-->>GlobalAddressResolver: URI (ServingRegion)
+    GlobalAddressResolver->>GlobalAddressResolver: GetEndpointCache(ServingRegion).AddressResolver
+
+    critical RegularAddressResolution(Implicit contract of dsr.RequestContext.ResolvedPartitionKeyRange population)
+        GlobalAddressResolver->>AddressResolver: ResolveAsync(DocumentServiceRequest)
+        AddressResolver-->>GlobalAddressResolver: PartitionAddressInformation
+    end
+
+    critical AnyPerpartitionOverrides
+        GlobalAddressResolver->>GlobalPartitionEndpointManager: TryAddPartitionLevelLocationOverride(DocumentServiceRequest)
+        GlobalPartitionEndpointManager-->>GlobalAddressResolver: (bool, DSR.RequestContext.RouteToLocation)
+
+        option YES
+            GlobalAddressResolver->>GlobalEndpointManager: ResolveServiceEndpoint(DocumentServiceRequest)
+            GlobalEndpointManager-->>GlobalAddressResolver: URI (ServingRegion)
+    end
+    GlobalAddressResolver->>GlobalAddressResolver: GetEndpointCache(ServingRegion)
+    GlobalAddressResolver->>AddressResolver: ResolveAsync(DocumentServiceRequest)
+    AddressResolver-->>GlobalAddressResolver: PartitionAddressInformation
+```
+
 ## Handler pipeline
 
 The handler pipeline processes the RequestMessage and each handler can choose to augment it in different ways, as shown in our [handler samples](../Microsoft.Azure.Cosmos.Samples/Usage/Handlers/) and also handle certain error conditions and retry, like our own [RetryHandler](../Microsoft.Azure.Cosmos/src/Handler/RetryHandler.cs). The RetryHandler will handle any failures from the [Transport layer](#transport) that should be [handled as regional failovers](#cross-region-retries).