Performance monitoring for streaming responses

[szokeasaurusrex]

Problem Statement

In the Django integration, if a user wishes to performance-monitor a streaming response, the Django integration currently ends the transaction before the entire streaming response is complete. See the following for more context: getsentry/sentry#64864 (comment).

Solution Brainstorm

The transaction should continue running until the streaming response is complete. We should either auto-detect a streaming response and automatically instrument the entire streaming response, or we should allow users to specify that they need the entire streaming response to be instrumented.

[sentrivana]

Closing in favor of #3736