[SPA] Setup new repo for the templates

[javiercn]

The new repo name is: https://github.com/dotnet/spa-templates

• We need to setup dependency flows from the asp.net core and into the SDK
• We need to move the code from src/ProjectTemplates/Spa.ProjectTemplates into this new repo.
• We need to produce packages and flow them into the SDK

• Populate the dotnet/spa-templates repo
• Use the new repo as a submodule in dotnet/aspnetcore (Use spa-templates repo as a submodule #34366 w/ fix in Correct spa-templates submodule #34499)
• Get dotnet/spa-templates to support dotnet build when built outside the dotnet/aspnetcore submodule
• Revert changes to src/submodules/Directory.Build.* files

[mkArtakMSFT]

@dougbu I've asked @terrajobst to setup the new repo. Will you then help us with getting it wired up in Arcade so that the dependencies flow properly. @javiercn will fill in the details in this issue shortly, so that it's clear what exactly is needed.

[dougbu]

• What versions need to flow and from where❔
• Will the new repo build using the Arcade SDK❔
• Are you asking me to also create the AzDO repo necessary for official builds❔

[mkArtakMSFT]

Talked some more regarding this and the decision is to have the new repo configured as a module for doptnet/aspnetcore.