Add Deploy 17.1.0-rc1 release notes

[ronaldbarendse]

📋 Description

Adds release notes for Umbraco Deploy 17.1.0-rc1:

• New @umbraco-deploy/backoffice NPM package (with a dedicated subsection describing what it exposes).
• Entity signs for queued entities.
• Environment name header app, including the queue count badge.
• User group description support (Umbraco CMS 17.2+).
• Exporting all supported entity tree roots (including the fix that allows transferring/restoring/exporting all members when AllowMembersDeploymentOperations is not None).
• Compatibility with the Umbraco CMS 17.4 change that makes IHostingEnvironment.ApplicationMainUrl nullable (umbraco/Umbraco-CMS#22307).

📎 Related Issues (if applicable)

N/A

✅ Contributor Checklist

I've followed the Umbraco Documentation Style Guide and can confirm that:

• Code blocks are correctly formatted.
• Sentences are short and clear (preferably under 25 words).
• Passive voice and first-person language ("we", "I") are avoided.
• Relevant pages are linked.
• All links work and point to the correct resources.
• Screenshots or diagrams are included if useful.
• Any code examples or instructions have been tested.
• Typos, broken links, and broken images are fixed.

Product & Version (if relevant)

Umbraco Deploy 17.1.0-rc1.

Deadline (if relevant)

Alongside the 17.1.0-rc1 release.

[github-actions]

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[sofietoft]

When will the 17.1 RC be released? Then I'll know when to publish these docs. Thanks 🙏

[ronaldbarendse]

When will the 17.1 RC be released? Then I'll know when to publish these docs. Thanks 🙏

It was released yesterday! Dates are always in the version headers, but I did forget to also put it in the PR description 😅

[sofietoft]

Ah, right! Forgot to check there ;)

I'll merge!