- Rename `anymail.backends.amazon_sesv2.EmailBackend`
to `amazon_ses`, making SES v2 the default.
- Rename the old `amazon_ses` backend to `amazon_sesv1`,
keeping it available. Add a deprecation warning.
- Alias `amazon_sesv2` to `amazon_ses`, with a
deprecation warning (for projects that opted
into v2 early under Anymail 9.1 or 9.2).
- Similar renaming on the test files.
- Update docs to assume v2 in most places
(other than migration-specific sections)
