Add ability to query for specifications through the REST API

How: Add additional "specificationCriteria" property in the body of the /api/v1.0.0/query endpoint

Why: Currently, there is no way of querying for data in specifications. This is however possible when using the Remoting API with a ComplexQuery. I believe that the REST API should have the same capabilities as the Remoting API.

For Who: This is mainly for developers creating integrations with inriver or other tools in which querying for specifications is useful.

Impact: High (because it enables developers to create solutions that do not depend on the Remoting API)

Additional context: I am in a situation in which upon a CVL value change need to react. When a CVL value changes, I need to find all Entities that have fieldtypes that use this CVL - this is possible using REST. I also need to find all Entities with specification field types using the CVL - this is not possible using REST, but can be done with Remoting.

An example of a request body could be:
{
"systemCriteria": [
{
"operator": "Equal",
"type": "EntityTypeId",
"value": "Item"
}
]
"specificationCriteria": [
{
"operator": "Equal",
"specificationFieldTypeId": "ColorSpecification",
"value": "blue"
}
],
}

It should work quite similarly to how the dataCriteria works today.

Please, add your suggestion and feedback above to add to the insights used by Product team when deciding priorities and direction of the Inriver PIM.