Provision to add new config options in sample config file

In Rocky we have added support for multiple backend as a EXPERIMENTAL
feature. However configuration options related to multiple backend
are not generated in sample config file due to some issue. We have
added below 2 new config options for multiple backend.

1. enabled_backneds (added in glance)
2. default_backend (added in glance_store)

Made provision to add all the above options to sample config
file.

Depends-On: https://review.openstack.org/#/c/603331/
Change-Id: Iff3db9fe31243e5b9610742c796fdca84c698bcf
Closes-Bug: #1793057

etc/oslo-config-generator/glance-api.conf

@@ -3,6 +3,7 @@ wrap_width = 80
 output_file = etc/glance-api.conf.sample
 namespace = glance.api
 namespace = glance.store
+namespace = glance.multi_store
 namespace = oslo.concurrency
 namespace = oslo.messaging
 namespace = oslo.db

glance/opts.py

@@ -60,6 +60,7 @@ _api_opts = [
         glance.common.wsgi.eventlet_opts,
         glance.common.wsgi.socket_opts,
         glance.common.wsgi.wsgi_opts,
+        glance.common.wsgi.store_opts,
         glance.image_cache.drivers.sqlite.sqlite_opts,
         glance.image_cache.image_cache_opts,
         glance.notifier.notifier_opts,