`externalDocs` support for the auto-generated PowerShell reference documents

[maisarissi]

1. Find a way of linking from the PowerShell reference page back to the API reference page.

2. Human written content in API reference page that describes the purpose of the cmdlet/api is not being migrated. Links also need to be migrated to PowerShell reference page.

• Extract the right information that we have in the API page:
  
  

• And than, use it as the first paragraph.
  

  The current information is being retrieved from the relationships session on the doc page:
  

3. Some parameters/properties are not bringing the right description from the API page. (Enum for sure, maybe others too)

• E.g., color in Update-MgUserCalendar (Update-MgUserCalendar - PowerShell Reference Docs // calendar resource type - Microsoft Graph Docs)

[georgend]

These all map to Operation descriptions in the OpenAPI:
PATCH on a collection: Autogenerate description when DeepInsertSupport or DeepUpdateSupport is present.
PATCH/PUT on a collection item: Use UpdateRestrictions.Description
GET on a collection: Use ReadRestrictions.Description.
GET on collection item: Use ReadRestrictions.ReadRestrictionByType.Description
POST on a collection: InsertRestriction.Description
DELETE on collection item: DeleteRestrictions.Description

OpenAPI PathItem descriptions are autogenerated and are used by the CLI tooling for things like e.g. mgc applications -h .

Relevant Capability Annotations:
https://github.com/oasis-tcs/odata-vocabularies/blob/758e454f012dd50de1f96a51953054ead7ad4656/vocabularies/Org.OData.Capabilities.V1.md#ReadRestrictionsType
https://github.com/oasis-tcs/odata-vocabularies/blob/main/vocabularies/Org.OData.Capabilities.V1.md#UpdateRestrictionsType

Actions:
@georgend to use ApiDoctor to inject from documentation into the CSDL metadata
@irvinesunday to implement conversion to OpenAPI for operation descriptions in OpenApi.Net.OData library.