Add templates to the Azure.Core library to make custom StatusMonitors easy to construct and use

It is the recommended pattern that service teams explicitly define the shape of their StatusMonitor. Update the existing templates so that

- There is a model template that contains required standard properties that can be used with spread or `is` to define the status monitor
- Add an operation template to take a StatusMonitor model from the user and produce an opeation to get the status monitor
- Update documentation to recommend this pattern in creating LRO operations

Start by locating the existing Azure.Core model and operation templates, then read the documentation for creating LRO operations. Confirm how templates accept user-defined StatusMonitor models and identify the expected standard properties. Done means both templates support the recommended pattern and the documentation explains how to use it.

Written by the indexing model from the issue text.