Log level resets to "0" after microceppd restarts

# Log level resets to "0" after microcephd restarts or host reboots
This issue is related to https://github.com/canonical/microceph/issues/239.

## What version of MicroCeph are you using ?
$ **lsb_release -a**
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 23.10
Release: 23.10
Codename: mantic

$ **sudo microceph --version**
ceph-version: 18.2.0-0ubuntu3~cloud0; microceph-git: 450240f5dd

## What are the steps to reproduce this issue ?

1. verify log level using command _sudo microceph log get-level_. In my case it always 0 (zero) after host reboots.
2. change log level to any other than 0 (zero), for example using next command: _sudo microceph log set-level 3_
3. verify that log level change is accepted using command _sudo microceph log get-level_. (actually microcephd continues producing debug level logs due to bug https://github.com/canonical/microceph/issues/239).
4. restart microcephd using command _sudo snap restart microceph.daemon_ and wait for several seconds until the microcephd restarts and initializes. You can also restart host instead of restarting microcephd service via snap.
5. verify log level using command _sudo microceph log get-level_.

## What happens (observed behaviour) ?
log level resets to "0" (zero) after microcephd restarts

## What were you expecting to happen ?
log level should remain the same as set in step 3 of "steps to reproduce" section above.

## Relevant logs, error output, etc.
### test shell script:
```
#!/bin/sh
echo ">>>" && \
echo "Current log level: $(sudo microceph log get-level)" && \
echo "Changing log level to 3" && sudo microceph log set-level 3 && \
echo "Log level has been updated to: $(sudo microceph log get-level)" && \
echo "Restarting microcephd" && sudo snap restart microceph.daemon && \
echo "Waiting for 10s" && sleep 10s && \
echo "Log level after restart: $(sudo microceph log get-level)" && \
echo "<<<"
```

### script output
>>>
Current log level: 0
Changing log level to 3
Log level has been updated to: 3
Restarting microcephd
Restarted.
Waiting for 10s
Log level after restart: 0
<<<

If it’s considerably long, please paste to https://gist.github.com/ and insert the link here.

## Additional comments.

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