Migrate rds_snapshot* modules and tests (ansible-collections#1453)

Migrate rds_snapshot* modules and tests

Depends-On: ansible-collections#1012
Depends-On: ansible-collections#1481
Remove rds_snapshot* modules and tests
These modules have been migrated to amazon.aws
Update runtime.yml with redirects to that collection
Update ignore files

Reviewed-by: Mike Graves <mgraves@redhat.com>
Reviewed-by: Bikouo Aubin <None>
Reviewed-by: Mark Chappell <None>