Improve dataplane bump workflow

[qmonnet]

Currently, we run workflow update-dp.yml whenever we push to the main branch, to update the dataplane repo to pull the latest changes. When doing so, we need to first wait for the build.yml workflow to complete, so that CI in dataplane can pull the new package. To do so, we sleep for 45 minutes in update-dp.yml.

Sleeping like this leads to inefficient usage of CI runners; and it's not guaranteed to work anyway, given that the build may occasionally take more than 3 hours. Instead, what we should do is move the step from update-dp.yml to workflow build.yml and run them after the package has been uploaded, if and only if the workflow was triggered by a push to main.