feat(constraint): add description for new entityId constraint type (#188

)

concepts.mdx

@@ -105,12 +105,13 @@ All constraints have a _property_, _type_, _operator_ and optionally a _value_.
 
 #### Constraint Types
 
-Currently 4 constraint types are available:
+Currently 5 constraint types are available:
 
 - **String** which allows you to check a string property of an entity
 - **Number** which allows you to check a number property of an entity (integer or float)
 - **Boolean** which allows you to check a boolean property of an entity such as `true` or `false`
 - **DateTime** which allows you to check a date or datetime property of an entity such as `2020-01-01` or `2020-01-01T00:00:00Z` ([RFC3339](https://datatracker.ietf.org/doc/html/rfc3339))
+- **EntityId** which allows you to check the `entityId` that was sent in the body of the `Variant` or `Boolean` request
 
 ![Constraint Types](/images/concepts/constraints_types.png)