Add on-demand option to k3d dev script

Package Merge Request

Package Changes

Adds --on-demand to k3d-dev.sh.

Default remains spot. With --on-demand, the script skips --instance-market-options so AWS launches a normal on-demand EC2 instance.

Package MR

N/A

For Issue

Closes #3294 (closed)

Upgrade Notices

N/A

Validation

• bats --jobs 4 --recursive tests/bats/
• live --on-demand cluster validation
• live default spot cluster validation