Clearify documentation around max_inflight_events

[tkaitchuck]

Problem description
There was some confusion in
#438

caused by the default parameter resulting in poor throughput.

Problem location

pravega-client-rust/python/src/stream_manager.rs

Line 407 in 73b46a6

/// By default the max inflight events is configured for 0. The users can change this value

Suggestions for an improvement
Make this more explicit in the documentation. And alter our examples to explicitly set the parameter rather than using the default of 0, to encourage thinking about it.