Fix CLM configuration error

[DavidePrincipi]

The "filter" field is optional, ensure it is present before setting the environment variable.

Nov 04 11:12:08 rl1.dp.nethserver.net agent@loki1[34817]: task/module/loki1/cb194da5-28c4-47b5-9df8-317b7b6fa786: set-clm-forwarder/10set is starting
Nov 04 11:12:08 rl1.dp.nethserver.net agent@loki1[34817]: Traceback (most recent call last):
Nov 04 11:12:08 rl1.dp.nethserver.net agent@loki1[34817]:   File "/home/loki1/.config/actions/set-clm-forwarder/10set", line 25, in <module>
Nov 04 11:12:08 rl1.dp.nethserver.net agent@loki1[34817]:     agent.set_env('CLOUD_LOG_MANAGER_FILTER', f"{request['filter']}")
Nov 04 11:12:08 rl1.dp.nethserver.net agent@loki1[34817]:                                                  ~~~~~~~^^^^^^^^^^
Nov 04 11:12:08 rl1.dp.nethserver.net agent@loki1[34817]: KeyError: 'filter'
Nov 04 11:12:09 rl1.dp.nethserver.net agent@loki1[34817]: task/module/loki1/cb194da5-28c4-47b5-9df8-317b7b6fa786: action "set-clm-forwarder" status is "aborted" (1) at step 10set

Refs NethServer/dev#7061