Add support for MR rebase/retry checkbox

What problem do you want to solve?

Renovate adds a checkbox to MRs to rebase/retry, but the proxy does not trigger a Renovate pipeline when the box is checked.

What is the proposed solution?

Update logic to look at changes in description and if this checkbox is found checked then trigger a renovate pipeline.

The renovate logic to determine if this checkbox was checked can be found here.