Create Integration Test for Extension Rest Requests

[dbwiddis]

The OpenSearch RestSendToExtensionRequest has a lot of key functionality for extensions but is not covered in tests. New integration tests should be written to:

• Validate proper JSON format of the response
• Validate that both routes and replaced routes produce the same output
• Validate that long-running requests return a proper timeout message
• Validate that unconsumed parameters on the extension side produce a correct unconsumed parameter message
• Validate that unconsumed content on the extension side produces a correct unconsumed content message