#7766966 Update index.tsx

Update the agency dashboard down time notifications email field to remove the text field and replace it with text indicating that the notification email address is the same as the account email address

Proposed Changes

• This PR removes the text field for the email address and updates the information associated with the text field to indicate that the email address used for notifications is the same as the associated account email address.

Testing Instructions

• Run git checkout update/update-agency-dashboard-notifications-email-field
• Run yarn start-jetpack-cloud
• Visit the dashboard at http://jetpack.cloud.localhost:3000/dashboard
• Click on the clock icon to open the down time monitor notifications settings
• Ensure that the email address text field has been removed and replaced with text indicating the email address is the account email address

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the “[Status] String Freeze” label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
• For changes affecting Jetpack: Have we added the “[Status] Needs Privacy Updates” label if this pull request changes what data or activity we track or use (p4TIVU-ajp-p2)?

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