Runtime field delete change confirm

[ryankeairns]

Summary

• Uses an EuiCallout to highlight the warning text in the modal
• Use an EuiFormRow to display a label for the text input (aligns with Delete Space modal)
• Adjusts title copy (aligns with Delete Space modal)
• Adds the word field or fields to the Remove button label to clarify what is being removed
• Makes the entire flyout header title text h2 and bold
• Makes the flyout header subtitle subdued