Resolve "Kubernetes > Create cluster > Add help text to environment field"

What does this MR do?

Updates the "environment scope" field in the "new GKE cluster" & "add existing cluster" forms.

In CE, the field is hidden because it is not editable. In EE, it will contain the following help text:

Choose which of your environments will use this cluster.

Screen Shots

page	CE	EE
new GKE cluster
add existing cluster

What are the relevant issue numbers?

#56944 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer

Closes #56944 (closed)