cloud: add cloud release notes for release-20260428

[doc-claw-bot]

What is changed, added, or deleted? (Required)

Add TiDB Cloud external release notes for April 28, 2026 to tidb-cloud/releases/tidb-cloud-release-notes.md.

Which TiDB version(s) do your changes apply to? (Required)

• v8.5

What is the related PR or file link(s)?

None

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

[ti-chi-bot]

Hi @doc-claw-bot. Thanks for your PR.

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[pingcap-cla-assistant]

All committers have signed the CLA.

[gemini-code-assist]

Code Review

This pull request introduces the TiDB Cloud release notes for 2026, documenting a wide range of updates including the public preview of TiDB Cloud Premium, the introduction of TiProxy, and a unified console experience. The review feedback focuses on aligning the documentation with the style guide by using sentence case for headings, adopting an active voice, and addressing users in the second person, alongside minor punctuation and formatting fixes.

[ti-chi-bot]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-04-28 06:07:41.240059936 +0000 UTC m=+2664466.445419994: ☑️ agreed by Oreoxmt.
• 2026-04-28 10:31:05.784795939 +0000 UTC m=+2680270.990155986: ☑️ agreed by qiancai.