Plottting-service health check to include reading file on IDAaaS

[Pasarus]

Right now the service does not check if the filesystem is accessible. It could be that a restart is required, to re-aquire the connection to the CephFS so we will force a restart by failing the health check if a file is unreadable.

There is a file at: /ceph/GENERIC/autoreduce/healthy_file.txt with the contents:
This is a healthy file! You have read it correctly!

Use it to check if it can read files correctly.