[#6771] Fix Attachment issue when it has a MemoryStream instance

[sw-joelmut]

Fixes #6771

Description

This PR fixes an issue with DLASE when a MemoryStream instance is being used as an Activity.Attachment, e.g. a file. The ReadTimeout issue is caused when trying to serialize the non-serializable MemoryStream instance.

Specific Changes

• Adds the AttachmentMemoryStreamConverter to serialize and deserialize a MemoryStream instance.
  • Serialize (WriteJson): It recursively searches and replaces all instances of MemoryStream to a serializable class, containing a type and a buffer array.
  • Deserialize (ReadJson): It recursivelly searches and converts all objects of type MemoryStream to a MemoryStream instance with the buffer array.
• Adds unit tests to cover cases previous to the JsonConverter addition, and using the JsonConverter.

Testing

The following images show the bot working, and the unit tests passing.

[sw-joelmut]

Im looking at the failing tests

[BruceHaley]

:heavy_check_mark: No Binary Compatibility issues for Microsoft.Bot.Schema.dll