[Feature Request] Notify renovate of a new package release to trigger run on dependent repositories

[rose-a]

Hi, I switched from dependabot-gitlab to renovate-on-prem because of it's awesome ability to group dependency updates.

There is one feature I am missing now:

dependabot-gitlab provides an API endpoint where you can notify it that there is a new release for a specific dependency, which then schedules runs for all repositories which use that dependency.

I have many private repositories which depend on each other (like described in #79), and this speeded up i.e. fixing a bug manifesting in application B which has its ultimate cause in dependency library A a lot, since it almost immediately results in an automatic PR in repo B after releasing a fixed version of A, and therefore you're only another couple of clicks away from updating application B after releasing the fix...

I think this would solve #79 entirely.