[SIMPL-30787] Document container-cluster configuration inputs

Add the cluster-configuration input reference the guide was missing: which inputs are mandatory, conditional or optional in each setup, a reusable minimum input set, and worked examples expressed in the format each setup already uses. No configuration schema or key naming is prescribed.

Retitle the subject sections so they no longer carry one story's AC numbering, and add a traceability section mapping SIMPL-30787 and SIMPL-30451 acceptance criteria onto them.

Changelog: added

README.md

@@ -35,7 +35,7 @@ distributed-execution/
 │   ├── work.py
 │   ├── requirements.txt
 │   └── Dockerfile
-├── documents/user-guide/           # AC1-AC4 documentation
+├── documents/user-guide/           # Guide, checklist and requirement traceability
 ├── yaml/                           # Working example configuration
 ├── tests/
 ├── Dockerfile