allow choosing prefer repodata format

[chisaato]

Problem description

For some 3rd repos, they may forgot to remove the older repodata file. here is an example

this is download from intel https://software.repos.intel.com/python/conda/linux-64
repodata.json is extracted from repodata.json.bz2 and repodata2.json is directly download and rename locally.

only repodata.json on the server has latest packages. so pixi can add some config to lock format for a channel

like this

channels = [
    "conda-forge",
    "pytorch",
   {url= "https://software.repos.intel.com/python/conda",format="json"},
]

[wolfv]

Thank you for pointing this out! Ideally this would be fixed by Intel ... I'll ask if they can do something about it. Thanks for also filing an issue with them!