Update the start command to use validate_schema (#82)

Closes #77

## By Submitting this PR I confirm:
- I am familiar with the [Contributing Guidelines](https://github.com/NVIDIA/AgentIQ/blob/develop/docs/source/advanced/contributing.md).
- We require that all contributors "sign-off" on their commits. This certifies that the contribution is your original work, or you have rights to submit it under the same license, or a compatible license.
  - Any contribution which contains commits that are not Signed-Off will not be accepted.
- When the PR is ready for review, new or existing tests cover these changes.
- When the PR is ready for review, the documentation is up to date with these changes.

Authors:
  - David Gardner (https://github.com/dagardner-nv)

Approvers:
  - Michael Demoret (https://github.com/mdemoret-nv)

URL: #82

Author: dagardner-nv

src/aiq/cli/commands/start.py

@@ -27,6 +27,7 @@
 from aiq.cli.type_registry import GlobalTypeRegistry
 from aiq.cli.type_registry import RegisteredFrontEndInfo
 from aiq.data_models.config import AIQConfig
+from aiq.utils.data_models.schema_validator import validate_schema
 from aiq.utils.type_utils import DecomposedType
 
 logger = logging.getLogger(__name__)
@@ -184,7 +185,7 @@ def invoke_subcommand(self,
         # Get the front end for the command
         front_end: RegisteredFrontEndInfo = self._registered_front_ends[cmd_name]
 
-        config = AIQConfig.model_validate(config_dict)
+        config = validate_schema(config_dict, AIQConfig)
 
         # Check that we have the right kind of front end
         if (not isinstance(config.general.front_end, front_end.config_type)):