feat: Consider SERVICE_BINDING_ROOT Env Var for Layered Bindings

[Johannes-Schneider]

Context

This PR extends the SapServiceOperatorLayeredServiceBindingAccessor to also consider the SERVICE_BINDING_ROOT environment variable for binding the root path of the mounted service bindings.
Hereby, we are supporting the Proposed CF Extension.

Feature Scope

• Consider the SERVICE_BINDING_ROOT env var whenever we are reading service bindings

Release Notes

Module: java-sap-service-operator

• Feature: The SapServiceOperatorLayeredServiceBindingAccessor now considers the SERVICE_BINDING_ROOT environment variable for finding the root location of mounted service bindings. If that variable is not defined, the accessor falls back to the default root location (/etc/secrets/sapbtp).

Definition of Done

• Feature scope is implemented
• Feature scope is tested
• Feature scope is documented
• Release notes are created