Improve failure output to make debugging /failure fixing in tests simpler

### Origin situation
I accidently defined a wrong type in my test (I used String.class instead of JsonFieldType.STRING) which led to a `resources.json` containing:

```json
, {
"attributes" : { },
"description" : "my text...",
"ignored" : false,
"path" : "content[].metaData.xyz",
"type" : "java.lang.String",
"optional" : true
}, {
```
which leads to gradle failure with:

```bash
Task openapi3 FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task 'openapi3'.
> unknown field type java.lang.string

```
That was all output.

Of course this is my fault, but to find the problem wasn't easy - at the beginning I did not recognize that the `resource.json` output inside `build/generated-snippets/myTargetFolder` is full used to generate openapi parts and there you can find the location of the problem etc. etc.

### Wanted
It would be nice to have
- the location of the problematic `resource.json` or
- the problematic test case, or
- the path/attributes or
- anything else that makes it simpler to locate the problematic part
inside the gradle output in failure case.