fix(cli): do not validate contexts in ado delete context

[AlessandroPomponio]

Summary

Refactors the context deletion logic to remove unnecessary Pydantic validation and simplify the code by directly accessing YAML configuration values instead of validating the entire ProjectContext model.

Resolves #819

Files Changed

📄 orchestrator/cli/resources/context/delete.py

Simplifies the context deletion flow by removing Pydantic model validation. Instead of validating the entire ProjectContext model from the YAML file, the code now loads the YAML as a dictionary and uses get_nested_value() utility to directly access the metadataStore.scheme field. This removes the dependency on pydantic and ProjectContext model, eliminates error handling for validation errors, and makes the code more lightweight since full model validation is unnecessary for the delete operation that only needs to check the database scheme type.