Download link should specify data format for LAPIS

[theosanderson]

Our download link is a simple link, with a LAPIS URL, which you can copy to use in other contexts. But if you use it in a web context, then often Accept headers are added that request JSON and so the query instead returns JSON. This just confused me while working on something. IMO we should add a dataFormat parameter to the LAPIS query (which LAPIS does support) so that the URL has consistent content returned in different settings.