download: Update maintenance page settings

[jcfr]

See https://discourse.slicer.org/t/maintenance-of-download-slicer-org-slicer-kitware-com-and-slicer-packages-kitware-com-planned-for-march-28th-2024-3-30pm-to-5-00pm-et/35155

[slicerbot]

download.slicer.org preview [branch: deploy_download_maintenance_preview]

:warning: The download preview is a static website generated using mock data [^1], is temporary and may be updated at anytime [^2]	Screenshot from https://deploy-download-maintenance-preview--slicer-org.netlify.app/download.html

[^1]: See front matter variable download_mock associated with https://raw.githubusercontent.com/Slicer/slicer.org/main/download.markdown [^2]: Due to limitation of Netlify preventing us from having multiple deploy previews associated with a single pull request and the impossibility of using repository secret in a workflow associated with a pull-request originating from forks, the deploy-download-preview site is only updated for pull request originating from this repository and will be overriden after another pull request is pushed or updated.

[slicerbot]

download.slicer.org preview [branch: deploy_download_preview]

:warning: The download preview is a static website generated using mock data [^1], is temporary and may be updated at anytime [^2]	Screenshot from https://deploy-download-preview--slicer-org.netlify.app/download_release_and_nightly.html	Screenshot from https://deploy-download-preview--slicer-org.netlify.app/download_only_release.html	Screenshot from https://deploy-download-preview--slicer-org.netlify.app/download_only_nightly.html
Screenshot from https://deploy-download-preview--slicer-org.netlify.app/download_release_and_nightly.html

[^1]: See front matter variable download_mock associated with https://raw.githubusercontent.com/Slicer/slicer.org/main/download.markdown [^2]: Due to limitation of Netlify preventing us from having multiple deploy previews associated with a single pull request and the impossibility of using repository secret in a workflow associated with a pull-request originating from forks, the deploy-download-preview site is only updated for pull request originating from this repository and will be overriden after another pull request is pushed or updated.