Use hubs in SignalR: Move all code examples to app project vers 7.0

This doc has a lot of inline code samples. Move the code to an app project and verify updated to 7.0.

A heads up that the scope of this work is a bit on the larger side and I will not know exactly how big until I get well into it:

* In some cases the code snippets have been written in the doc as minimal general examples but not compliable code, such as missing required params or other required items expected within the method in order to work within an app sample.

* The code samples span the following client types and differing hub server+client scenarios:
*.NET Client
*Typescript client
*Java client

* The context of how some of the snippets were supposed work in a larger app scenario are missing in places and the code out of date.

It is possible that for this issue/step, I may need to just add what is needed to the snippets to compile, add what would be expected in the methods to work and create compliable snippet hub classes, reviewed by the dev team. This appears to be the route already taken with some other hub class samples on the samples repo. Then as the dev team is able to take time with me to work out full client + Hub app samples for those scenarios as they intended to work, we can get additional app samples for those scenarios added to the samples repo.

Related to issue #27996

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#### Document Details

⚠ *Do not edit this section. It is required for learn.microsoft.com ➟ GitHub issue linking.*

* ID: 1387f556-b4b7-70f9-5bd0-f0bccc597689
* Version Independent ID: fb016cdc-d281-6b5b-7466-2c718e7274b4
* Content: [Use hubs in ASP.NET Core SignalR](https://learn.microsoft.com/en-us/aspnet/core/signalr/hubs?view=aspnetcore-7.0)
* Content Source: [aspnetcore/signalr/hubs.md](https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/signalr/hubs.md)
* Product: **aspnet-core**
* Technology: **aspnetcore-signalr**
* GitHub Login: @bradygaster
* Microsoft Alias: **bradyg**

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