docs: add release notes ocis 8.1.0

[mmattel]

This PR adds release notes for ocis 8.1.0

[DeepDiver1975]

Release notes for oCIS 8.1.0 look good — correct version, coherent structure, valid xrefs (build + lint green). One scope point:

• package-lock.json (whole file): this "docs: add release notes" PR also carries unrelated lockfile churn — package.json is unchanged, so no direct dep was intentionally bumped. The diff is incidental npm install regeneration: transitive/dev bumps (qs 6.14→6.15.3, follow-redirects 1.15.11→1.16.0, minimatch, side-channel, streamx, thread-stream, etc.) plus npm re-hoisting nested node_modules entries to top level.
• Harmless but out of scope for a docs PR. Suggest dropping the package-lock.json change (git checkout origin/master -- package-lock.json) and keeping this PR to the .adoc, or splitting the lockfile refresh into its own PR so it's reviewed on its own.

Not blocking the content — just flagging the mixed scope.

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