DAG validation with JSON schema in YAML editor

[yohamta]

Overview
Add the JSON schema-based validation to the DAG(YAML) editor.

JSON schema
The schema file is available at:
https://raw.githubusercontent.com/daguflow/dagu/main/schemas/dag.schema.json

Implementation
Configure react-monaco-editor to use the provided JSON schema file. The component to modify is here.

[vhespanha]

I'd like to take a look at this one, can you assign?

[vhespanha]

Opened a draft PR, if the approach I took for the implementation seems correct, I can further enhance it.

PR #659