osd_types, Objecter: make recovery_deletes feature create a new interval

osd_types, Objecter: make recovery_deletes feature create a new interval

This is needed to create a single place to regenerate the missing set
- at the start of a new interval where support for recovery deletes
changed.

The missing set is otherwise not cleared, so it would need to be
rebuilt in arbitrary places if e.g. an osd not supporting it went down
and restarted with support, or if we used a feature flag command to
trigger rebuilding the missing set.

Signed-off-by: Josh Durgin <jdurgin@redhat.com>