Designate does not delete the zone-files on the back-end when zone is
deleted. This results in thousands leftover zone files on backend e.g.
bind. Add option in designate zone delete API to force clean/delete
zone-files on the back-end. This option is restricted for admin or
owner roles.
Closes-Bug: 1966517
Change-Id: Ic7b8fee4d4702b0632774d32542b23d7d2a8c253