UE pass on Host in a Windows Service doc

[scottaddie]

https://docs.microsoft.com/aspnet/core/host-and-deploy/windows-service

• UE edit
• Update template name referenced in https://docs.microsoft.com/en-us/aspnet/core/host-and-deploy/windows-service?tabs=aspnetcore2x#prerequisites No longer relevant.
• Update sample for 2.1 (CreateWebHostBuilder approach).
• Remove UseApplicationInsights calls.
• Display necessary using statements in code snippets. They're in the sample app.
• Address customer comments Except for the "namespace" remark, they're not actionable, and the remark on namespaces is covered by the sample app.

[guardrex]

@scottaddie Some of this work was covered by the updates on #6860 and some of the patches thereafter. If you want to transfer this to me and email me the reader comments, I'll have the bandwidth later to react to the comments and take a look at the using statement item.

[scottaddie]

@guardrex Assigned and emailed you the verbatim / SkyRay info.