feat(build): add utils.deploy.env.add build plugin API#6918

ndhoule wants to merge 9 commits intomainnetlify/build:mainfrom

nathanhoule/ex-27-add-api-to-netlifybuild-for-registering-deploy-variablesnetlify/build:nathanhoule/ex-27-add-api-to-netlifybuild-for-registering-deploy-variablesCopy head branch name to clipboard