The following lines were previously improperly forming a payload pipeline in the $https operator tests.

We'd like to ensure that the payload pipeline works by:

1. adding body to MockHttpClient::Request so we can MockHttpClient::expect a request with a specific body payload
2. Re-add the $project stages to the following inner pipelines:

https://github.com/10gen/mongo/blob/75b6b3aa4387ded461c0e2c56e3331faa93c0412/src/mongo/db/modules/enterprise/src/streams/exec/tests/https_operator_test.cpp?plain=1#L611-L612

https://github.com/10gen/mongo/blob/75b6b3aa4387ded461c0e2c56e3331faa93c0412/src/mongo/db/modules/enterprise/src/streams/exec/tests/https_operator_test.cpp?plain=1#L1359-L1360