Host specific keyrings for `RadosGW` service.

# Issue report

## What version of MicroCeph are you using ?
This is an enhancement bug.

## What are the steps to reproduce this issue ?

1. Setup 3 node MicroCeph cluster with disks
2. Enable RGW daemons on all 3 nodes

## What happens (observed behaviour) ?
The RGW daemons use the same `client.radosgw.gateway` keyring.

## What were you expecting to happen ?
Each RGW instance should have it's own keyring file.