feat(http client builder): Add max_concurrent_requests setter

[sydhds]

No description provided.

[niklasad1]

This "feature" has been removed and has no effect anymore.

We/I forgot to remove the max_concurrent_request field on the builder because it was not ergonomic to use in async to code to wait until one would get MaxSlotsExceeded ...

For now you enforce the "limit" yourself for example with a semaphore/channel or something like that. Ideally with a channel bounded channel to provide backpressure which is much more ergonomic to deal with in async code.

However, I reckon that the API is not really uniform anymore compared to the "ws-client/async-client" APIs which provides max_concurrent_requests. So we could add "it back" to http-client but with backpressure