Feature: expose jetstream client by reference

[Ferrany1]

#1481 1481

[Jarema]

@Ferrany1 thanks for the contribution.

However, not only it is a breaking change for not practical reason.
This is common pattern in Rust to have cheaply clone'able handle.

This also introduces some lifetime problems.

[caspervonb]

Not sure what the motivation is, since client is clonable?

Could have:

fn client_ref(&self) -> &Client;

But would have to be tied to lifetime of self.