Fix modes allowed in CLI (#764)

## Summary

## Checklist
- [ ] Added Unit Tests
- [ ] Covered by existing CI
- [x] Integration tested
- [ ] Documentation update



<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Bug Fixes**
- Improved the handling of the `--mode` command-line option to ensure
all available choices are displayed as strings. This enhances
compatibility and usability when selecting modes.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: david-zlai

api/python/ai/chronon/repo/run.py

@@ -98,7 +98,7 @@ def set_defaults(ctx):
     default="dev",
     help="Running environment - default to be dev",
 )
-@click.option("--mode", type=click.Choice(MODE_ARGS.keys()), default=RunMode.BACKFILL)
+@click.option("--mode", type=click.Choice([str(k) for k in MODE_ARGS.keys()]), default=RunMode.BACKFILL)
 @click.option("--ds", help="the end partition to backfill the data")
 @click.option("--app-name", help="app name. Default to {}".format(APP_NAME_TEMPLATE))
 @click.option(