fix: Correctly deserialize outer envelope when processing messages relayed through EventBridge

[96malhar]

Issue

• EventBridge -> SQS. Failed to create a MessageEnvelop #97
• DOTNET-7432

Description of changes:
This is a sample SQS message when messages are forwarded by EventBridge

{
  "version": "0",
  "id": "961ac8a3-a4ee-0e17-d8d9-36c81ae29955",
  "detail-type": "AWS.Messaging.IntegrationTests.Models.ChatMessage",
  "source": "/aws/messaging",
  "account": "000000000",
  "time": "2024-03-25T20:39:11Z",
  "region": "us-west-2",
  "resources": [],
  "detail": {
    "id": "526d5466-5f51-42ce-a64b-8a220a7f1b71",
    "source": "/aws/messaging",
    "specversion": "1.0",
    "type": "AWS.Messaging.IntegrationTests.Models.ChatMessage",
    "time": "2024-03-25T20:39:10.8491344+00:00",
    "data": "{\"MessageDescription\":\"Test1\"}"
  }
}

The detail property is sent as a JSON object and not as a string. Invoking JsonElement.GetString on this node throws an InvalidOperationException.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.