RFC: update activation logic or option to only activate when biome.json is found

[cdaringe]

Problem

I operate in many projects, and biome and _other formatter_s have minor behavior differences.

I want biome in projects that call for it, and other formatters in projects that call for those.

Discussion

Can we update the activation logic s.t. this extension only triggers on detection of biome.json or package.devDependencies.@biome/*?

Should be feasible with: https://code.visualstudio.com/api/references/activation-events#workspaceContains