[Spring 2026] Email Sender and Domain table

# Context
- Juno Dashboard currently does not have a way to register senders and domains for the email service
- We need a table for each of them and a way to delete/create senders and domains

# Requirement

- [ ] Create a table for email senders and a table for email domains (see file bucket or provider table for style reference)
- [ ] Have those tables in page called Configurations accessible through a tab under Email in the sidebar (see picture)

- [ ] Add get endpoints in the API Gateway and email service to get senders and domains from Sendgrid
- Senders: `curl -X GET -H "Authorization: Bearer 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" -H "Content-Type: application/json" 'https://api.sendgrid.com/v3/verified_senders'`
- Domains: `curl -X GET -H "Authorization: Bearer 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" -H "Content-Type: application/json" 'https://api.sendgrid.com/v3/whitelabel/domains'`

- [ ] Add e2e tests and update SDK as needed

- [ ] Add sender and domain creation form and use existing email service SDK methods to perform those operations

## PR requirement:

- [ ] Create your SendGrid account and api key
- [ ] Video demo showing the tables and creating new senders/domain operations, and refer to the Sendgrid Dashboard to show that the operations succeeded