Add support to configure scheduler_default_filters

Add new config option: `scheduler-default-filters`.
This is unset by default, so manila retains the default value for
scheduler_default_filters.

Closes-Bug: #1998200
Change-Id: I82eddf8f54d954f6d930265ec8612398f4cc90a0
(cherry picked from commit 2cfb486f41)

src/config.yaml

@@ -83,3 +83,11 @@ options:
       Setting multiple arbitrary configuration variable for manila.conf file.
       Any configuration paramiters is comma-separated.
       Zero or one spaces are allows between tokens.
+  scheduler-default-filters:
+    type: string
+    default: ""
+    description: |
+      List of comma-separated filter class names to use for filtering hosts
+      when not specified in the request.
+      If not set, the default Manila filters will be used. Those might change
+      based on OpenStack release.

src/templates/rocky/manila.conf

@@ -28,6 +28,10 @@ debug = {{ options.debug }}
 # Number of workers for OpenStack Share API service. (integer value)
 osapi_share_workers = {{ options.workers }}
 
+{% if options.scheduler_default_filters -%}
+scheduler_default_filters = {{ options.scheduler_default_filters }}
+{% endif -%}
+
 {% include "parts/section-transport-url" %}
 
 {% for key, value in options.user_config_flags.items() -%}