Merge postman collections for docker/k8 using environment variables

Merge postman collections for docker/k8 using environment variables

- Moved dmi-stub-2 requests from kubernetes folder to CPS-NCMP/Inventory/Southbound (dmi)
- Added Liveness & Readiness folder with health checks for CPS and DMI-Stub services
- Updated all DMI URLs to use environment variables ({{DMI_HOST}}:{{DMI_PORT}})
- Renamed environments: "CPS Environment Docker" and "CPS Environment k8s-linux-minikube"
- Added DMI_HOST_2 and DMI_PORT_2 variables for dmi-stub-2 support
- Updated README with Kubernetes setup instructions for Linux/Windows

Issue-ID: CPS-3058
Change-Id: I9045c72873eaaca316138d5303945d8441ded1b2
Signed-off-by: shikha0203 <shivani.khare@est.tech>