Implement a validation service for workflows

Research both Monaco out-of-the-box validation (using JSON schemas) and CNCF sdk-typescript validation to implement a service that validates serverless workflow files and return the result with all errors and warnings.

At first this service should work only for JSON files, but in the future can work for YAML as well.

The validation should be automatically called 2 seconds (parameterized by extension configuration) after a change in the editor.