(feat) enable local builds

[rbliss]

This feature enables creating a release in other build environments outside of Netlify. I've used the local term to be consistent with internal naming, and Netlify patterns.

When using the netlify CLI to run a build on other CI systems (Github Actions for example), enabling this flag will override the default behavior of preventing "local" builds (i.e. builds outside of Netlify) from creating a release.