Add YAML schema for Citrus DSL

**User story**
We should add a YAML schema for the Citrus test DSL. Similar to Yaml Schema of Camel which you can put at the beginning of your Yaml DSL like:

```
 # $schema: https://github.com/apache/camel/blob/camel-4.13.0/dsl/camel-yaml-dsl/camel-yaml-dsl/src/generated/resources/schema/camelYamlDsl.json
 
- route:
  [...]
```
