Implement Validation, Error Handling, and Backward Compatibility

[ShohamBit]

Background
With a new configuration system that merges both file-based and flag-based settings, it’s crucial to ensure that all inputs are valid and that any issues are surfaced in a user-friendly manner. We also need to maintain support for deprecated fields (like capture and signatures) for backward compatibility, ensuring a smooth transition for users who rely on older configurations.

Tasks

• Implement thorough validation checks for all configuration options after merging.
  • Check for invalid values, missing required fields, and unsupported combinations.
• When invalid configurations are detected, produce clear, actionable error messages.
  • Indicate which option is invalid and why.
  • Suggest corrective steps if possible.
• Ensure backward compatibility with deprecated fields:
  • Process and accept deprecated fields and flags.
  • Show warnings to inform users these options are deprecated and may be removed in the future.
• Add unit and integration tests that cover:
  • Invalid configurations and expected error messages.
  • Correct handling of deprecated settings.
  • Proper functionality with valid configurations.

Acceptance Criteria

• Any invalid or conflicting settings are caught with helpful error messages.
• Deprecated options still work but display clear warnings.
• Tests confirm that validation and backward compatibility behave as expected under various scenarios.

Why This Matters
Proper validation and error handling enhance user trust and usability. By clearly indicating what went wrong and why, we help users fix issues quickly. Supporting deprecated options with warnings allows for a gradual transition, preventing user frustration and disruption.

[yanivagman]

Part of #4453