Update the docs workflow and fix failures

[erinecon]

Applicable spec: ISD-3255

Overview

Add documentation workflow to the repository and fix linkcheck and Vale errors.

Rationale

The Makefiles existed in the repository but the workflow wasn't set up.

Juju Events Changes

None

Module Changes

None

Library Changes

None

Checklist

• The charm style guide was applied
• The contributing guide was applied
• The changes are compliant with ISD054 - Managing Charm Complexity
• The documentation for charmhub is updated
• The PR is tagged with appropriate label (urgent, trivial, complex)
• The CHANGELOG.md is updated with user-relevant changes.

There are no user-relevant changes apart from minor documentation changes.
Either discourse-gatekeeper will update the documentation on Charmhub or I will upon approval of this PR.

[github-actions]

Unused entries in .trivyignore

Image: ghcr.io/canonical/content-cache:4d42a3657e84ab3c6a320166c41090f5e990340b-_latest_amd64

The following CVEs are in .trivyignore but not ignored by Trivy anymore:

• CVE-2024-45338
• CVE-2025-22874