Add explanation of close modes to documentation

Parallel Consumer has two shutdown modes - with draining and without - add explanation of those to documentation along with timeout options and how they apply.

Locate the existing documentation for consumer shutdown or close behavior, then read the relevant Java API definitions for the two shutdown modes and timeout options. Document draining and non-draining shutdown, including how the timeout settings apply; done means both modes and their timeout behavior are explained clearly.

Written by the indexing model from the issue text.