Update release note titles to match Grafana

[heitortsergent]

What?

Update release note titles to match other Grafana projects. This will make the version number render correctly once it's listed in grafana.com/docs.

Checklist

• I have used a meaningful title for the PR.
• I have described the changes I've made in the "What?" section above.
• I have performed a self-review of my changes.
• I have run the npm start command locally and verified that the changes look good.

• I have made my changes in the docs/sources/next folder of the documentation.
• I have reflected my changes in the docs/sources/v{most_recent_release} folder of the documentation.

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