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 option 2 from above to sample config
file.

Change-Id: I63571e4a8f85003e304f16653d60cbd38e6b6bde
Partial-Bug: #1793057

glance_store/multi_backend.py

@@ -98,6 +98,21 @@ Related Options:
 _STORE_CFG_GROUP = 'glance_store'
 
 
+def _list_config_opts():
+    # NOTE(abhishekk): This separated approach could list
+    # store options before all driver ones, which easier
+    # to generate sampe config file.
+    driver_opts = _list_driver_opts()
+    sample_opts = [(_STORE_CFG_GROUP, _STORE_OPTS)]
+    for store_entry in driver_opts:
+        # NOTE(abhishekk): Do not include no_conf store
+        if store_entry == "no_conf":
+            continue
+        sample_opts.append((store_entry, driver_opts[store_entry]))
+
+    return sample_opts
+
+
 def _list_driver_opts():
     driver_opts = {}
     mgr = extension.ExtensionManager('glance_store.drivers')

setup.cfg

@@ -47,6 +47,7 @@ glance_store.drivers =
 
 oslo.config.opts =
     glance.store = glance_store.backend:_list_opts
+    glance.multi_store = glance_store.multi_backend:_list_config_opts
 
 console_scripts =
     glance-rootwrap = oslo_rootwrap.cmd:main