Complex lint rule: apilintValuesIncluded

[tim-lai]

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from #2193 (comment)

@char0n on the lint side of things, do we have a way to lint/validate that a default value is present within the enum list? e.g. per: If the [enum](https://github.com/OAI/OpenAPI-Specification/blob/main/versions/3.1.0.md#serverVariableEnum) is defined, the value MUST exist in the enum's values.

We don't. We'll have to create one. The closer we have is apilintKeysIncluded function. This new one is going to be apilintValuesIncluded.

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