can not join additional node to cluster

# Issue report

## What version of MicroCeph are you using ?
18.2.4 reef (stable)

Use this section to describe the channel/revision which produces the unexpected behaviour.

I had to forcefully remove a node due to a hardware failure. Afterwards I wanted to join a new node with the previous node name and ip address, unfortunately it run in a timeout. Now I'm getting the following error:
Error: failed to record mon db entries: failed to record mon host: This "config" entry already exists
I then tried to add a new node with a new ip address and name, unfortunately same result.

## What are the steps to reproduce this issue ?

1. install new node with 'sudo snap install microceph --channel reef/stable'
2. create token on a cluster node with 'sudo microceph cluster add '
3. join cluster on new node with 'sudo microceph cluster join '
4. Error: failed to record mon db entries: failed to record mon host: This "config" entry already exists

## What happens (observed behaviour) ?
Error: failed to record mon db entries: failed to record mon host: This "config" entry already exists
…

## What were you expecting to happen ?
new node should have joined the cluster
…

## Relevant logs, error output, etc.

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

## Additional comments.
I've realized that in the ceph.conf entry 'mon host = ' only the ip of the new hosts are present, the ip's of the two currently operating nodes are missing
…