[native] generic function to send requests to the MPSC

Summary: We have a channel that handles outgoing streaming requests. We factor out some of the error handling here to avoid repeating ourselves.

Test Plan: cargo build, tested later when we send requests to Identity service

Reviewers: tomek, karol, atul

Reviewed By: tomek

Subscribers: ashoat, abosh

Differential Revision: https://phab.comm.dev/D4904