Add minimal support for v3 code generation

### Scope

- [x] https://github.com/asyncapi/java-spring-cloud-stream-template/issues/336
- [x] https://github.com/asyncapi/java-spring-template/issues/308
- [x] https://github.com/asyncapi/java-template/issues/118
- [x] https://github.com/asyncapi/nodejs-template/issues/215
- [x] https://github.com/asyncapi/python-paho-template/issues/189

### All templates

The following is a list of all the templates that eventually would have to be migrated. This is not the scope of this issue but I'm pasting it here just for reference.

- https://github.com/asyncapi/dotnet-nats-template/issues/384
- https://github.com/asyncapi/go-watermill-template/issues/243
- https://github.com/asyncapi/java-spring-cloud-stream-template/issues/336
- https://github.com/asyncapi/java-spring-template/issues/308
- https://github.com/asyncapi/java-template/issues/118
- https://github.com/asyncapi/nodejs-template/issues/215
- https://github.com/asyncapi/nodejs-ws-template/issues/294
- https://github.com/asyncapi/python-paho-template/issues/189
- https://github.com/asyncapi/ts-nats-template/issues/545

Start by reviewing the five checked template issues linked under Scope, then compare them with the reference list of templates still to be migrated. The issue does not name source files or tests; completion would require defining the v3 code-generation scope and confirming the relevant template migrations.

Written by the indexing model from the issue text.