ci: fix helm diff in case of forks

[fcjack]

What this PR does / why we need it:

The workflow for the helm-diff has the last job as post a comment in the PR with the diffs for each scenario.
When the PR is coming from a fork, we don't have permission to write to the PR in the workflow and the fork CI won't be able to get the right secrets to generate github tokens.

Then we are skipping this job in case of forks, but all the outputs are still accessible via github artifacts in the workflow run.

Special notes for your reviewer:

The change to use the vault secrets was made because is a recommendation from platform team to store the secrets inside vault instead of using the github secrets.

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
  • Note that Promtail is considered to be feature complete, and future development for logs collection will be in Grafana Alloy. As such, feat PRs are unlikely to be accepted unless a case can be made for the feature actually being a bug fix to existing behavior.
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• If the change is deprecating or removing a configuration option, update the deprecated-config.yaml and deleted-config.yaml files respectively in the tools/deprecated-config-checker directory. Example PR

[poyzannur]

lgtm

[loki-gh-app]

Helm Diff Output - Summary

Single Binary Scenario

Default Values Scenario

Ingress Values Scenario

Legacy Monitoring Scenario

Simple Scalable AWS Kube IRSA Scenario

[github-actions]

Helm Diff Output - Summary

Single Binary Scenario

Default Values Scenario

Ingress Values Scenario

Legacy Monitoring Scenario

Simple Scalable AWS Kube IRSA Scenario

[svennergr]

LGTM 👍