Release prep v9.1.0

[github-actions]

Automated release-prep through pdk-templates, corrected by hand.

The automation regenerates the entire tag history from scratch on every run, which dropped the v9.0.0 withdrawal note (explaining that 8.2.1 was mistakenly published as a patch despite dropping Puppet 7 support) and invented a bogus v8.2.1 section with no indication it was withdrawn.

Fixed:

• CHANGELOG.md keeps the full accurate history unchanged (v9.0.0 and below, exactly as on main) with an accurate v9.1.0 entry added on top, including a note that this release raises the minimum puppetlabs/concat requirement to 7.4.0 (from Eliminate Workaround for Sensitive Data #607), which can break dependency resolution for environments pinned to an older concat.
• HISTORY.md, the base file the changelog is built from, now also carries that same v9.0.0-and-older content, so it survives future release-prep runs regardless of what happens to CHANGELOG.md.

Please verify before merging:

• last nightly run is green
• Changelog is readable and has no unlabeled pull requests
• Ensure the changelog version and metadata version match

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