983 Adds infra for email config and dispatch

[eastandwestwind]

Purpose

Prove we can store email configs and send dummy MFA email using mailgun (actually implements much of the work needed for CRUD/db layer for email config)

Changes

• Adds APIs for email config
• Adds db migration
• Adds associated db models, schemas, and enums
• Adds to postman collection

Follow-ups / associated tickets:

• Unit tests will be done here- Add unit tests for EmailConfig APIs #1086
• Docs will be added here- Add docs for email config #1064
• Celery queue- Add email tasks to a separate Celery queue #1088
• Store org name for emails Leverage organization name for email service #1087

Checklist

• Update CHANGELOG.md file
  • Merge in main so the most recent CHANGELOG.md file is being appended to
  • Add description within the Unreleased section in an appropriate category. Add a new category from the list at the top of the file if the needed one isn't already there.
  • Add a link to this PR at the end of the description with the PR number as the text. example: #1
• Applicable documentation updated (guides, quickstart, postman collections, tutorial, fidesdemo, database diagram.
• If docs updated (select one):
  • documentation complete, or draft/outline provided (tag docs-team to complete/review on this branch)
  • documentation issue created (tag docs-team to complete issue separately)
• Good unit test/integration test coverage
• This PR contains a DB migration. If checked, the reviewer should confirm with the author that the down_revision correctly references the previous migration before merging
• The Run Unsafe PR Checks label has been applied, and checks have passed, if this PR touches any external services

Ticket

Fixes #983

[TheAndrewJackson]

Does EmailServiceDetails need IS_SERVICE_DETAILS when EmailServiceDetailsMailgun has is_eu_domain?

[TheAndrewJackson]

Looks good! Great job at making it modular. It should be straight forward to add more email providers in the future.