Add COS integration

[mthaddon]

When running this charm in a production setting it would be useful to be able to integrate it with COS to get metrics/dashboards for the application.

[reneradoi]

Resolved with #61.

As of revision 29 in latest/edge, this charm now supports COS lite. Please make sure to pull the new image when updating, e.g. with juju refresh ... --resource redis-image=ghcr.io/canonical/charmed-redis:7.2.5-22.04-edge.

Redis metrics can be found in the dashboard Redis Dashboard for Prometheus Redis Exporter under General.

Other than that, the following changes are included in this revision:

• update to version 7.2.5 of redis
• redis now runs in appendonly mode by default in order to avoid data loss (see also: https://redis-stack.io/docs/management/persistence/)