nixos/release-notes: deprecate services.pdns-recursor.settings

  [not recommended by upstream](https://docs.nextcloud.com/server/30/admin_manual/installation/system_requirements.html)

  and thus doesn't qualify as default.

- PowerDNS Recursor has been updated to version 5.1.2, which comes with a new YAML configuration format (`recursor.yml`)

  and deprecates the previous format (`recursor.conf`). Accordingly, the NixOS option `services.pdns-recursor.settings`

  has been renamed to [old-settings](#opt-services.pdns-recursor.old-settings) and will be provided for backward compatibility

  until the next NixOS release. Users are asked to migrate their settings to the new [yaml-settings](#opt-services.pdns-recursor.old-settings)

  option following this [guide](https://doc.powerdns.com/recursor/appendices/yamlconversion.html).

  Note that options other than `services.pdns-recursor.settings` are unaffacted by this change.

- Nextcloud's default FPM pool settings have been increased according to upstream recommentations. It's advised

  to review the new defaults and description of

  [](#opt-services.nextcloud.poolSettings).