Support conditional expression to evaluate based on the data type for a given field

[dlvenable]

Background

Some processors we only want to run when the field has a certain type.

Proposal

I propose creating a new operator within the Data Prepper expression language: typeof.

This could be used to determine if a given field has a certain type.

For example:

/myfield typeof string

Additionally, this approach could support inheritance.

For example, the following could be true:

25 typeof integer
25 typeof number
25.5 typeof double
25.5 typeof number

Types

Data Prepper doesn't have have a consistent concept of types. However, we should have some core types. We can base these on what we already have for the convert entries processor.

data-prepper/data-prepper-plugins/mutate-event-processors/src/main/java/org/opensearch/dataprepper/plugins/processor/mutateevent/TargetType.java

Lines 21 to 25 in 24bbbf1

	INTEGER("integer", new IntegerConverter()),
	STRING("string", new StringConverter()),
	DOUBLE("double", new DoubleConverter()),
	BOOLEAN("boolean", new BooleanConverter()),
	LONG("long", new LongConverter());

Alternative

One alternative is to add a new function.

$type(/myfield) == 'string'

However, this would not work so well with inheritance.

[kkondaka]

Another option is to provide a function in expressions like isType(/field, "string") or isTypeOf(/field, "string").

[dlvenable]

Completed by: #4500