Final draft for v1.31 release

[npolshakova]

What type of PR is this:
/kind cleanup
/kind documentation

What this PR does / why we need it:

This PR refactors and fine-tunes all the release-notes for v1.31.0, and does the following:

• Cleanups up md file
• Cleans up the json files to make sure the website has the revised release notes

The major themes link to the upcoming release article will not be included as we are moving away from having major themes being a thing in future releases.

[everpeace]

Hi, I'm KEP-3619 owner. May I add this release note item

- Added Node.Status.Features.SupplementalGroupsPolicy field which is set to true when the feature is implemented in the CRI implementation (KEP-3619) ([#125470](https://github.com/kubernetes/kubernetes/pull/125470), [@everpeace](https://github.com/everpeace)) [SIG API Machinery, Apps, Node and Testing]

next to L.64?

sig-release/releases/release-1.31/release-notes/release-notes-draft.md

Line 64 in b3f1422

- Support fine-grained supplemental groups policy (KEP-3619), which enables fine-grained control for supplementary groups in the first container processes. You can choose whether to include groups defined in the container image(/etc/groups) for the container's primary uid or not. ([#117842](https://github.com/kubernetes/kubernetes/pull/117842), [@everpeace](https://github.com/everpeace)) [SIG API Machinery, Apps and Node]

This item is user-facing which is related to KEP-3619. And, this item is actually included in rc.0 release note: https://github.com/kubernetes/kubernetes/blob/master/CHANGELOG/CHANGELOG-1.31.md?plain=1#L186

[jsafrane]

Would it be possible to re-generate release note / add it manually from kubernetes/kubernetes#124815? I added release-note field there today.

It could be one of the "Urgent Upgrade Notes". Chance that someone has the removed feature gates enabled is very low, but if they do, then they need to remove them from cmdline of all Kubernetes components.

I am adding a note to the release blog here: https://github.com/kubernetes/website/pull/47281/files#r1703842605

[k8s-ci-robot]

PR needs rebase.

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[neoaggelos]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: neoaggelos, npolshakova

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