Parameter types are used for validation. These types are consistent
with [google.protobuf.Value][].
Values:
PARAMETER_TYPE_UNSPECIFIED (0):
Not specified. No validation will be
performed.
STRING (1):
Represents any string value.
NUMBER (2):
Represents any number value.
BOOLEAN (3):
Represents a boolean value.
NULL (4):
Represents a null value.
OBJECT (5):
Represents any object value.
LIST (6):
Represents a repeated value.