[Doc]: Get-AzCosmosDBMongoDBCollectionThroughput returns 404 if run on a shared throughput collection

### Description

As titled, if the command is run on a shared throughput collection, we would only get the generic 404 error. The behavior is the same for both PS and bash CLI.

```text
Get-AzCosmosDBMongoDBCollectionThroughput: Entity with the specified id does not exist in the system. More info: https://aka.ms/cosmosdb-tsg-not-found
```

The ask here is to improve the self-help error message to make it stand out more.

首先，在 PowerShell 中针对共享吞吐量 collection 重现 Get-AzCosmosDBMongoDBCollectionThroughput，并使用等效的 bash CLI 命令进行重现，然后跟踪通用 404 自助错误的生成位置。当错误能够明确识别共享吞吐量场景，并在两种命令行体验中提供更有用的指导时，即视为完成。

由索引模型根据 Issue 内容生成。