Feat/provide list of sending domains

[andrewleith]

Summary | Résumé

This PR updates the sending domain admin page to use a list of verified sending domains from AWS instead of a drop down list which could allow users to enter invalid domains into.

Since this lists rarely changes the request to SES is cached for 5 minutes so we don't send too many requests.

Related cards

• Celery crash if bad sending domain notification-planning#1363

Before - textbox

After - dropdown

Test instructions | Instructions pour tester la modification

• Login as an administrator
• Navigate to a service
• Go to Settings
• Go to the Sending domain row and click Change
  • Ensure the list of domains are in a dropdown
• Select a different domain
• Save your setting
• Send yourself a test email
  • Ensure the sending domain is the one you selected

[github-actions]

🧪 Review environment

https://m5nrumtltpawaqnq247ljuifoq0ocyll.lambda-url.ca-central-1.on.aws/

[sastels]

Is it easy to clear this from the cache, ie when we add a new one to AWS? (waiting 5 minutes is fine if this isn't already baked in somehow)

[jzbahrai]

I tested this locally and it worked, it doesn't work on admin preview though.