fix: Running the demo for extension charts

[chrisburr]

This pull request updates the run_demo.sh script to improve tool management and clarify the use of custom Helm charts. The most significant changes are the switch to using arkade for downloading required binaries, and the renaming and enhanced handling of the custom chart path option. These changes streamline the setup process and make the script more robust and user-friendly.

Tool management improvements:

• Replaced manual downloading of kind, kubectl, and helm with arkade, which now handles downloading these tools (as well as yq) into the .demo directory, reducing system dependencies and simplifying the script logic. (run_demo.sh)

Helm chart customization enhancements:

• Renamed the --chart-path option to --extension-chart-path for improved clarity, and updated all related help messages and error handling to match the new name. (run_demo.sh) [1] [2]
• When an extension chart is specified, automatically indents the generated values file under a new diracx top section using yq, ensuring compatibility with umbrella charts. (run_demo.sh)