Allow running of `netlify build` without linking site

When trying out plugins there is some unnecessary friction for users to test stuff out locally. One of those bits of friction is the requirement to netlify link before being able to run a local build.

Which problem is this feature request solving?

netlify build
Could not find the site ID. Please run netlify link.

Describe the solution you'd like

Allow running of netlify build without linking site.

netlify build should work in local projects without needing a remote Netlify site.

This makes trying & building plugins easier. It also will help with testing flows for plugins.

Can you submit a pull request?

Yes