chore: use new notary api

[gruyaume]

Description

Here we adapt the Notary K8s charm the the new Notary API. Doing so, we centralize the request creation and parsing using the new _make_request function.

We also improve some struct and function names for standardization. For example:

• get_certificate_requests_table -> list_certificate_requests
• post_csr -> create_certificate_request

Why I added Grafana lint exclusions

The CI is now failing at the grafana lint stage for a reason unrelated to my change. The grafana dashboard linter recently added logql linting. They don't version the tool and we use the latest version, hence why our CI was passing and is now failing on Grafana lint.

I added the following two Grafana lint exclusions:

• target-logql-rule:
• target-logql-auto-rule:

We should likely address those in the future.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that validate the behaviour of the software
• I validated that new and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules