[SB] Document support for Workload Resource Mapping

This feature is for the servicebinding.io API group.

• Need an assembly and a concept module covering what Workload Resource mapping is and why do we need to use this.
• Probably also a procedure module or at least an example in any related SBO procedures/steps on how to use this.
• Need to link the Creating custom resources from a file page under the Additional resources section of the assembly.