chore(kumactl): upgrade grafana/promtail to 3.3.2 in observability manifests

[bartsmykla]

Motivation

I know we plan to remove kumactl install observability eventually, but I think we should update its components for now, especially if it’s easy to do. Once the versions are more current, Renovate can take care of updates going forward.

Implementation information

Upgraded grafana/promtail from 2.4.1 to 3.3.2 in the Kubernetes manifest used by kumactl install observability. No configuration changes were needed, but removed readOnly: true from the /var/lib/grafana/plugins volume mount to allow Grafana to install the grafana-lokiexplore-app plugin. Tested locally to ensure everything works.

Supporting documentation

Related to: #11693

[github-actions]

Reviewer Checklist

🔍 Each of these sections need to be checked by the reviewer of the PR 🔍:
If something doesn't apply please check the box and add a justification if the reason is non obvious.

• Is the PR title satisfactory? Is this part of a larger feature and should be grouped using > Changelog?
• PR description is clear and complete. It Links to relevant issue as well as docs and UI issues
• This will not break child repos: it doesn't hardcode values (.e.g "kumahq" as an image registry)
• IPv6 is taken into account (.e.g: no string concatenation of host port)
• Tests (Unit test, E2E tests, manual test on universal and k8s)
  • Don't forget ci/ labels to run additional/fewer tests
• Does this contain a change that needs to be notified to users? In this case, UPGRADE.md should be updated.
• Does it need to be backported according to the backporting policy? (this GH action will add "backport" label based on these file globs, if you want to prevent it from adding the "backport" label use no-backport-autolabel label)