feat(files): Expose chunked upload config via capabilities

[provokateurin]

Summary

Part of https://github.com/nextcloud/server/issues/47682. https://github.com/nextcloud-libraries/nextcloud-upload/pull/1444

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• [ ] Tests (unit, integration, api and/or acceptance) are included
• [ ] Screenshots before/after for front-end changes
• [ ] Documentation (manuals or wiki) has been updated or is not required
• [ ] Backports requested where applicable (ex: critical bugfixes)