Adapt init jobs to be able to reset also the main branch

We may want to perform other/extra operations for the `main` branch, like removing files, setting up other version and so on.

We should add an extra param to init jobs to specify that a reset on this branch is necessary. And call the main init job with that param.

Finally, the `prepare-release-branch` should call it, in order to tell the main branch that it needs a reset.