Fix: Set default values for traits in VelaUX

[am6737]

• Addressed the issue where default values for traits (including "cpuscaler", "hpa", "resource", "k8s-update-strategy") were not being set properly.

Description of your changes

Fixes #650

I have:

• Read and followed KubeVela's contribution process.
• Related Docs updated properly. In a new feature or configuration option, an update to the documentation is necessary.
• Run yarn lint to ensure the frontend changes are ready for review.
• Run make reviewableto ensure the server changes are ready for review.
• Added backport release-x.y labels to auto-backport this PR if necessary.

Special notes for your reviewer

Traits with default values, such as "cpuscaler," "hpa," "resource," and "k8s-update-strategy," require some input to trigger the onChange event before the properties can be set correctly. To address this, I called onChange during the initialization phase to ensure the default values are set properly.

I realize that this approach may not be the most elegant solution, so I'm open to any suggestions for a better implementation or alternative ways to handle default values more effectively.