[New article]: How to register and use a custom implementation of IResourceMonitor

### Proposed topic or title

Custom implementation of IResourceMonitor

### Location in table of contents.

New articled in the Resource Monitoring section or a new paragraph in docs/core/diagnostics/diagnostic-resource-monitoring.md

### Reason for the article

It is not documented at all how to create, register, and use a custom implementation of the IResourceMonitor interface, despite the fact the interface is `public` which means users can have the custom implementation of it if they want to. It is not documented why the custom implementation might be needed either.

### Article abstract

Guidance how and why have a custom implementation of the IResourceMonitor interface

### Relevant searches

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