Disable the squash option from the cascade MR

[jmini]

When a ucascade Merge Request is merged manually, using the [ ] squash commits option is really bad, since it does not preserve the merge commit (that is the reason why the tool was created in the first place)

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Work-around:

It is possible to disable the "Squash" option for all MR in a project:

But this is a little bit extreme, since squashing commit might be something the users want to have in regular MR in a project.

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Required change in GitLab: https://gitlab.com/gitlab-org/gitlab/-/issues/290042

Once this feature is available, the auto MR should be configured in a way that it is not possible to squash the MR when merging it.