Fix randomly generated input inside Lime tests

Inside kogito-apps "org.kie.kogito.explainability.explainability.integrationtests.pmml", some Lime tests use auto-generated values (LimeExplainer#getPerturbedInputs)
Generated values are numbers, but in some test (e.g. PmmlRegressionCategoricalLimeExplainerTest) required field are string and - in some cases - only specific string are allowed (e.g. categoricalVariablesRegression.pmml:

    <DataField name="x" optype="categorical" dataType="string">
      <Value value="red"/>
      <Value value="green"/>
      <Value value="blue"/>
      <Value value="orange"/>
      <Value value="yellow"/>
    </DataField>
    <DataField name="y" optype="categorical" dataType="string">
      <Value value="classA"/>
      <Value value="classB"/>
      <Value value="classC"/>
    </DataField>

Please ensure that generated values are valid for the given field