Change saver_strategy value to String

Symbols in configuration values are problematic because Symbols do not
roundtrip through JSON.  Since the API now exposes Settings, it's not
possible to set Symbols as values.  The saver_strategy was fixed in
ManageIQ/manageiq#17168 to support String
values, and the next step is to remove all Symbols from the Settings.

ManageIQ/manageiq#17201
https://bugzilla.redhat.com/show_bug.cgi?id=1558031

config/settings.yml

@@ -61,13 +61,13 @@
     :enabled_deployments_caching: true
     :inventory_collections:
       # Strategy for saving, another allowed is :batch, doing batch SQL queries [Graph refresh only]
-      :saver_strategy: :default
+      :saver_strategy: default
   :azure_network:
     # Same options as in :azure, applied for a network manager
     :inventory_object_refresh: false
     :allow_targeted_refresh: true
     :inventory_collections:
-      :saver_strategy: :default
+      :saver_strategy: default
 :http_proxy:
   :azure:
     :host: