Allow block map cache size modification. (#35667)

The VDO Ansible module currently cannot modify the block map cache
size (but can configure the block map cache size for new volumes).
Add the "Block map cache size" parameter to the list of modifiable
parameters.

lib/ansible/modules/system/vdo.py

@@ -570,6 +570,7 @@ def run_module():
         # The 'vdo status' keys that are currently modifiable.
         statusparamkeys = ['Acknowledgement threads',
                            'Bio submission threads',
+                           'Block map cache size',
                            'CPU-work threads',
                            'Logical threads',
                            'Physical threads',