Add release announcement field to the Communications handbook

[kfess]

What type of PR is this:

/kind documentation

What this PR does / why we need it:

Add documentation for the release_announcement field in the release blog frontmatter to the Communications handbook.

This field is being introduced in kubernetes/website#54885 to support the automated release series page generation. The release series pages (e.g., /releases/1.35/) will automatically link to the corresponding release announcement blog post using this frontmatter field.

Which issue(s) this PR fixes:

None

Special notes for your reviewer:

The release series pages (e.g., https://kubernetes.io/releases/1.35/) are now auto-generated from existing data (kubernetes/website#54041). To automatically display a link to the release blog on these pages, PR (kubernetes/website#54885) is trying to add support for the release_announcement field in the blog frontmatter.

As suggested in kubernetes/website#54885, this PR updates the handbook so future Comms leads know to add this field.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: kfess
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Details

Needs approval from an approver in each of these files:

• release-team/role-handbooks/communications/OWNERS

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[rytswd]

/hold

We are in the middle of the cycle for v1.36, and would want to keep the handbook changes to minimum.
We will keep in mind about this new frontmatter handling in the upcoming release announcement though 👍

FYI @chadmcrowell

[kfess]

Sure! Would be great if you could revisit this once the v1.36 release is done. Thanks!