Add "Not" predicate operator in the Segment rules

[dabeeeenster]

We should have an "Add AND NOT" as per below:

Would also mean updating https://github.com/Flagsmith/flagsmith-engine

[kyle-ssg]

Added frontend under flag "not_operator", presumed format would be type:"NOT". The flag allows for adding an array of supported clientside evaluation SDKs (see staging for an example, leaving empty will remove the tooltip).

[
  {
    "type": "ALL",
    "rules": [
      {
        "type": "ANY",
        "rules": [],
        "conditions": [
          {
            "operator": "EQUAL",
            "property": "test",
            "value": "test"
          }
        ]
      },
      {
        "type": "NOT",
        "conditions": [
          {
            "property": "test",
            "operator": "EQUAL",
            "value": "test2"
          }
        ]
      }
    ],
    "conditions": []
  }
]

[khvn26]

As discussed internaly, the proposed operator should actually be "NONE" (and is already supported by engine implementations).