Remove statefulness from charm configuration

[dariofaccin]

Context

The charm should avoid to be stateful whenever possible.
In particular, configuration files should not be part of a PVC.
This can be achieved with the following steps.

Rock

The underlying rock needs to be modified so that the configuration path is owned by _daemon_:

mlmd:
  override-build:
    ...
    # make config dir
    mkdir -p $CRAFT_PART_INSTALL/config

non-root-user:
  plugin: nil
  override-prime: |
    craftctl default
    install -d -o 584792 -g 584792 -m 770 \
      config

Charm

In the metadata.yaml any storage and mounts reference needs to be removed.
In the charm, any check on storage availability needs to be removed.
Unit tests might to be updated to remove harness.attach_storage() call if present.

What needs to get done

1. Update rock
2. Update charm
3. Backport change

Definition of Done

1. Rock is updated
2. Charm is updated
3. New rock is integrated
4. Tests are passing
5. Change is backported

[syncronize-issues-to-jira]

Thank you for reporting your feedback to us!

The internal ticket has been created: https://warthogs.atlassian.net/browse/KF-8442.

This message was autogenerated

[MattiaSarti]

Addressed by #169