Add global.json with proper SDK version

Hi, could you add `globlal.json` to each template to fix .NET SDK version? After .NET 7 was released it is used by default and Fable fails building in this case. Even if you have both v6 and v7 installed, the 7th is used if no global.json.

`global.json`
```json
{
"sdk": {
"version": "6.0.407",
"rollForward": "latestFeature"
}
}
```
When Fable & Lit are ready for .NET 7 you will update the version.

Start by inspecting the repository's templates and identify each template that needs a global.json file. Use the requested SDK version 6.0.407 with latestFeature roll-forward, then verify that the Fable templates build with the .NET 6 SDK instead of defaulting to .NET 7.

Written by the indexing model from the issue text.