[AVM Question/Feedback]: Align diagnostic settings implementation for cross referenced and nested resources

### Description

The implementation of diagnostic settings applied to resources related to the main resource (nested or cross referenced) should be aligned and possibly simplified.

- List modules applying diagnostic on related resources and propose a consistent implementation for all
- Parameter names should be aligned (e.g., sometimes we have `pipDiagnostic` sometimes `publicIPDiagnostic`)
- Update guidelines in the wiki

Initial list:
- natgateways and virtual network gateways cross reference PIP and specify pip diagnostic settings parameters
- azure firewall and bastion host cross reference PIP and do not specify pip diagnostic settings parameters, they are implemented directly into the cross referenced module
- VM and VMSS apply diagnostic on pip and nics in a different way as they do not cross reference pip and nic modules. They specify diagnostic settings parameters for both pip and nic
> Note: VMSS pip diagnostic implementation is probably not working (to be tested)

Note: Diagnostic on cross referenced should also import shared common types

Start by comparing diagnostic implementations in the natgateways, virtual network gateways, Azure firewall, bastion host, VM, and VMSS modules, then test the noted VMSS public IP diagnostic behavior. Review how cross-referenced resources import shared common types and how parameter names differ. Done means a documented, consistent approach across the listed modules, aligned parameter names, and updated wiki guidance.

Written by the indexing model from the issue text.