Improve automation script to deal with "logic" conflicts

Currently the automation script that merges/rebases (MAISTRA-2717) creates an issue when the merge fails. If the merge succeeds, a PR is created. This PR should be created with the `auto-merge` label, so, if all tests succeed, it's going to be merged automatically by prow/tide.

In this bootstrap phase, we are not applying this auto-merge label, so the PR must be manually approved by a maintainer in order to be merged.

After this bootstrap phase, we would like to be able to track some special files, or directories, that, when changed upstream, would raise a flag for us maintainers. When this happens, the auto-merge label would not be applied, and the maintainers would be tagged to review the PR and approve it manually.

For example, in the case of Envoy, we would like to be aware when upstream touches BoringSSL-related code so we can manually inspect if this affects our OpenSSL port.