Use descriptions from restrictions annotations for operation descriptions

[irvinesunday]

We should use the restrictions capability annotations in the CSDL for the operations descriptions in the generated OpenAPI doc. For example, given the below restrictions annotations for the User entity type in the Graph metadata:

In the converted OpenAPI document, the operation description would be emitted as below:

The green highlights indicate descriptions retrieved from the restrictions annotations .

[maisarissi]

microsoftgraph/msgraph-sdk-powershell#876 has dependency on this feature.