Add v0.31.0 to the releases doc

[AlanGreene]

Changes

/kind documentation

Submitter Checklist

As the author of this PR, please check off the items in this checklist:

• Docs included if any changes are user facing
• Tests included if any functionality added or changed
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  functionality, content, code)
• Has a kind label. You can add one by adding a comment on this PR that contains /kind <type>. Valid types are bug, cleanup, design, documentation, feature, flake, misc, question, tep
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Release Notes

NONE

[briangleeson]

/lgtm

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[AlanGreene]

All of the checks are stuck, closing and reopening to see if that shakes them loose… 🤞