Errors Not Reported by Mongo ARM creation

1. Create a Mongo collection that triggers an error. Example: Try creating a mongo collection with a shard key `/id`
2. Get back a cryptic `response.text()` is not a function error message

The issue is this line here: https://github.com/Azure/cosmos-explorer/blob/99c6a7ebcc7a03761d3af1f757513ad439ef1f8f/src/Common/MongoProxyClient.ts#L460-L463

The catch clause has an implicit `any` type on response. But in this case, it is not an instance of `Response`. It is a RP specific error format: https://github.com/Azure/cosmos-explorer/blob/99c6a7ebcc7a03761d3af1f757513ad439ef1f8f/src/ResourceProvider/ResourceProviderClient.ts#L184

TypeScript 4.0 has a fix for this https://devblogs.microsoft.com/typescript/announcing-typescript-4-0-beta/#unknown-on-catch

cc @vchske

Start at src/Common/MongoProxyClient.ts around lines 460-463 and compare the RP-specific error format in src/ResourceProvider/ResourceProviderClient.ts around line 184. Reproduce the shard-key collection creation error and verify that the resulting message reports the underlying resource-provider error instead of the cryptic response.text() error.

Written by the indexing model from the issue text.