[docs]: Explain NestingType for Parallel and Map including observability trade-offs.

[dhegberg]

URL/Location

aws-durable-execution-docs/docs/sdk-reference/operations/parallel.md

Line 177 in a575cba

- `nesting` (optional) `NestingType.NESTED` (default) or `NestingType.FLAT`. `FLAT`

Describe What's Incorrect or Lacking

The current documentation references NestingType and the reduced observability but does not explain the use and trade-off.

Suggested Improvement

Add information to the advanced examples on 1) how/when to use NestingType and 2) document the observability trade-offs.

Additional Context

No response