[k8s][vm] Add content to release notes landing page

[a-velasco]

The Release notes landing page is currently empty.

This could be a good location for a high-level overview of the charm release process and artifacts.

[syncronize-issues-to-jira]

Thank you for reporting your feedback to us!

The internal ticket has been created: https://warthogs.atlassian.net/browse/DPE-9499.

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