Kubernetes Agent Registration dialog reloads the page when Enter is pressed

What does this MR do and why?

This MR fixes the bug when clicking enter during the agent creation reloaded the page.

Screenshots or screen recordings

How to set up and validate locally

To enable KAS in your GDK, follow the first part of this documentation:

1. Add the following settings in the gdk.yml

   gitlab_k8s_agent:
     enabled: true

2. gdk update

3. gdk reconfigure

4. gdk restart

When KAS is enabled the agent feature is available through GDK.

1. Visit Infrastructure -> Kubernetes clusters.
2. Select Connect a cluster (agent).
3. In the modal select Select an agent or enter a name to create new dropdown using the keyboard.
4. Type the name of the new agent and press enter.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Review progress:

• UX review
• frontend developer review
• frontend maintainer review

Related to #356584 (closed)