Add new openapi-normalizer rule REFACTOR_ALLOF_WITH_PROPERTIES_ONLY

[wing328]

Add new openapi-normalizer rule REFACTOR_ALLOF_WITH_PROPERTIES_ONLY.

When set to true, refactor schema with allOf and properties in the same level to a schema with allOf only and, the allOf contains a new schema containing the properties in the top level.

FYI @OpenAPITools/generator-core-team

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