fix: update cos-tool permissions to adhere to cis hardening rules

[lucabello]

Issue

Closes #208.

Solution

Fix the cos-tool permissions according to the linked issue (removing the write permission from others).

Warning

I had to bump the cos_agent library because of a linting error which was auto-fixed by tox -e fmt.

We change the cos-tool permissions with path.chmod(0o777) in multiple places:

• lib/charms/loki_k8s/v1/loki_push_api.py
• lib/charms/prometheus_k8s/v1/prometheus_remote_write.py
• lib/charms/grafana_k8s/v0/grafana_dashboard.py
• lib/charms/prometheus_k8s/v0/prometheus_scrape.py

We need three PRs in Prometheus, Loki and Grafana to fix those libraries:

• fix: update cos-tool permissions to adhere to cis hardening rules prometheus-k8s-operator#664
• fix: update cos-tool permissions to adhere to cis hardening rules grafana-k8s-operator#371
• fix: update cos-tool permissions to adhere to cis hardening rules loki-k8s-operator#485

I manually changed the library files, packed the charm, and tested with the juju ssh grafana-agent/X -- sudo find / -xdev -type f -perm -002 command, and no file with too many permissions is returned anymore.

Testing Instructions

charmcraft pack
juju deploy ./(grafana-agent-charm)
juju deploy zookeeper --base ubuntu@22.04
juju relate grafana-agent zookeeper

# wait for it to settle

# Look for files with too many permissions (see issue)
# Make sure this returns nothing
juju ssh grafana-agent/X -- sudo find / -xdev -type f -perm -002

[lucabello]

I will un-draft this as soon as the 3 linked PRs are merged.