feat: improve API spec to match implementation (planning#1788)

spec/destination-api.yaml

spec/endpoints/destinations/index.yaml

spec/endpoints/destinations/uuid.yaml

spec/headers/cache-control-no-cache.yaml

spec/schemas/create-destination.yaml

spec/schemas/destination-name.yaml

spec/schemas/destination-private-or-public.yaml

spec/schemas/destination-private-parts.yaml

spec/schemas/destination-private.yaml

spec/schemas/destination-update-private.yaml

spec/schemas/destination-update.yaml

spec/schemas/jwks-with-paging.yaml