Support negative matches

What does this MR do?

This adds support in only/except:variables: support for != and !~ operators.

This is the most naive approach. For example:

($AA == "AAA") && ($BB == "CCC") && ($DD == "XXX")

except:
  variables:
    - $AA != "AAA"
    - $BB != "CCC"
    - $DD != "XXX"

related https://gitlab.com/gitlab-org/gitlab-ce/issues/61900

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Style guides