keystring
Key is the label key that the selector applies to.
operatorstring
Operator represents a key's relationship to a set of values.
Valid operators are In, NotIn, Exists and DoesNotExist.
valuesarray of strings
Values is an array of string values. If the operator is In or NotIn,
the values array must be non-empty. If the operator is Exists or DoesNotExist,
the values array must be empty.