We're working on converting all plugins into packages, which turns
almost all code in the repository into a package except for things like
the `test` and `x-pack/test` directories. The problem we ran into is
that the alerting api-integration test plugins are being migrated to
packages but they are currently consuming a handful of helpers from the
parent `../lib` directory. This doesn't work, as packages can only
import other packages and the `../lib` directory isn't in a package,
it's just free-floating `x-pack/test` code. To fix this I've moved the
necessary components out of `common/lib` and into `packages/helpers`
which is importable via `@kbn/alerting-api-integration-helpers` and
updated all the uses to access this new package.
