Gremlin query - Apache TinkerPop - HelloWorld execution example

@mailtoach79 to put an example i.e. a Step executing gremlin query.
Either via a `string` body or via `$PATH:`

This is already supported by the framework. 👍

But if a specialized `place-holder` needed like below-
e.g. `$GREMLIN.QUERY.FILE:`, then it has to be created.
_(Please raise an issue for this if needed)_

Mr Uma has to suggest !

The final example will look like below-
```
{
"scenarioName": "Gremlin HelloWorld query",
"steps": [
{
"name": "execute_gremlin",
"url": "/tinkerpop/gremlin",
"operation": "POST",
"request": "g.V().hasLabel('airport').groupCount().by('country')",
"assertions": {
//query response for select country,count(country) from airports group by country;
}
}

]
}
```

No file or test is named. Start by locating the repository's existing YAML/JSON declarative-step examples and the entry point for REST examples, then compare their structure with the proposed Gremlin scenario. Done means adding a runnable HelloWorld Gremlin example with a clear response assertion, or documenting that the existing string/path request support is sufficient.

Written by the indexing model from the issue text.