Preserve snake_case while generating service spec jsons

[raamb]

As reported by Abdulrahman Semrie

Hi everyone. So I was having issues with testing of the moses-service and annotation-service through the dApp lately. After much debugging, I found out the issue occurs when there is an underscore in a field name of a message in the *proto* definition of the service. In this case, the DApp sends an empty string for that field and this will trigger an error on the service side. To reproduce the issue  I have deployed two versions of the annotation service. The first which is named *annotation-service* has an underscore in the field names and it fails with an error. The second one named *annotation-service-test* has no underscore in any of the field names and it works as expected.

Here are the model hash for the services:
   - annotation-service: `-----------------------------------`
   - annotation-service-test: `---------------------------------`

This issue occurs only from the dApp and it works fine from the `snet cli`.

The DApp get the service definition from this service which in turn uses protobuf to load the proto files. Protobufjs by default converts snake_case to camelCase. See protobufjs/protobuf.js#564

In order to preserve case, proposing to set the global flag on protobufjs as described protobufjs/protobuf.js#608

@vforvalerio87 @tesYolan