feat: make sharded repodata enabled by default

[ruben-arts]

Improves: #3271

Since we've been testing it for a long time already I think we can confidently make this the default.

The second question is, are we going to make https://prefix.dev/conda-forge the default channel as well to give users the best possible experience? 🤔

[Hofer-Julian]

Thanks!

[baszalmstra]

We can do the same in rattler!

[pavelzw]

are we going to make https://prefix.dev/conda-forge the default channel

if you do this, this should be considered a breaking change as then eventual mirror configurations for https://conda.anaconda.org won't work anymore

maybe a warning should be printed if you only have conda.anaconda.org in your mirror config (to something else than prefix.dev) and once do the switch