Supporting build:wait

[Naoto-Ida]

Hi y'all, thanks for building the Percy test runner for Storybook :)
I've been playing around with it for the past few days and really seeing potential.

Just some background info; we currently use Bitbucket Server and cannot move to Bitbucket Cloud.
We run the percy commands in our CI, but currently can't let Bitbucket or our CI know that a Percy build has been completed.

Therefore, I came up with this idea to integrate Percy testing into our CI after reading the percy build section of the docs.

Run PERCY_TOKEN=X yarn percy storybook ./storybook-static
then wait for yarn percy build:wait STORYBOOK_BUILD_ID to return, then proceed with other things.

Is it possible to have something like this out of @percy/storybook?