Add support for testing SSE (Server-Sent Events)

[ashitaprasad]

Tell us about the task you want to perform and are unable to do so because the feature is not available
SSE is gaining widespread popularity due to LLMs. We should support this feature.

See related discussion point 2 in #112

[mmjsmohit]

Would like to start working on this issue.
The package I am planning to use for this is sse by the Dart Team.

Would update with the initial draft of the design sketch in sometime.

P.S. I am looking forward to following the same approach as in #258 and #215, hence would love to get some feedback on them!

[ashitaprasad]

Sure @mmjsmohit.

[mmjsmohit]

Here's the proposed the design sketch.