Port System.Net docs for .NET 9 APIs

[carlossanlop]

Below is the list of APIs that still show up as undocumented in dotnet-api-docs and were introduced in .NET 9.

Full porting instructions can be found in the main issue.

This task needs to be finished the day before the RC2 snap (September 15th).

Undoc APIs as of RC1 (2024/10/01): #106789 (comment)

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[carlossanlop]

Reopening as there are two APIs in RC1 that need to get ported (2024/10/01):

API	Summary	Parameters	TypeParameters	ReturnValue
P:System.Net.WebSockets.ClientWebSocketOptions.KeepAliveTimeout	Missing	NA	NA	NA
P:System.Net.WebSockets.WebSocketCreationOptions.KeepAliveTimeout	Missing	NA	NA	NA