proxmox: deprecate old compatibility feature flag (#6836)

* proxmox: deprecate old compatibility feature flag

* add changelog frag

* bump deprecation to 10

changelogs/fragments/6836-proxmox-deprecate-compatibility.yml

@@ -0,0 +1,2 @@
+deprecated_features:
+  - proxmox - old feature flag ``proxmox_default_behavior`` will be removed in community.general 10.0.0 (https://github.com/ansible-collections/community.general/pull/6836).

plugins/modules/proxmox.py

@@ -183,6 +183,10 @@ options:
         are used when the values are not explicitly specified by the user. The new default is V(no_defaults),
         which makes sure these options have no defaults.
       - This affects the O(disk), O(cores), O(cpus), O(memory), O(onboot), O(swap), and O(cpuunits) options.
+      - >
+        This parameter is now B(deprecated) and it will be removed in community.general 10.0.0.
+        By then, the module's behavior should be to not set default values, equivalent to V(no_defaults).
+        If a consistent set of defaults is needed, the playbook or role should be responsible for setting it.
     type: str
     default: no_defaults
     choices:
@@ -621,7 +625,8 @@ def main():
         description=dict(type='str'),
         hookscript=dict(type='str'),
         timezone=dict(type='str'),
-        proxmox_default_behavior=dict(type='str', default='no_defaults', choices=['compatibility', 'no_defaults']),
+        proxmox_default_behavior=dict(type='str', default='no_defaults', choices=['compatibility', 'no_defaults'],
+                                      removed_in_version='9.0.0', removed_from_collection='community.general'),
         clone=dict(type='int'),
         clone_type=dict(default='opportunistic', choices=['full', 'linked', 'opportunistic']),
         tags=dict(type='list', elements='str')