Suggestion: add-on recommendations in settings

VS Code has workspace recommendations, which is a nice way to get a project up and running quickly after cloning a repo. The user is notified of recommended extensions and can quickly install them.

I think it would be nice if the VS Code add-on for LuaLS would support the same. Perhaps settings could be extended with something like:

```json
{
"properties": {
"workspace": {
"recommendations": ["love2d"]
}
}
}
```

And then after installing the LuaLS extension, a window could pop-up showing the recommended add-on(s), to be installed with the click of a button.

Begin by locating the extension manifest and settings-related entry points, then verify how VS Code represents workspace extension recommendations and installation prompts. Define the supported recommendation format and prompt behavior, with completion shown by recommendations being surfaced and installable in a cloned workspace.

Written by the indexing model from the issue text.