refactor: move more package worker logic to manager

lib/manager/docker/package.js

lib/manager/index.js

lib/manager/npm/package.js

lib/workers/package/index.js

test/manager/docker/__snapshots__/package.spec.js.snap

test/manager/docker/package.spec.js

test/manager/npm/__snapshots__/package.spec.js.snap

test/manager/npm/package.spec.js

test/workers/package/__snapshots__/index.spec.js.snap

test/workers/package/index.spec.js