conda workflows: re-enable sharded repodata

[jameslamb]

Description

Issues with sharded repodata publishing for the rapidsai conda channel blocked the 26.06 release, so we opted out of that metadata in #564

It should be restored by reverting that PR, once the issues described in rapidsai/cugraph#5542 (comment) are resolved.

Benefits of this work

• sharded repodata provides noticeable speedups to conda and rattler-build (see Enable and cache Conda repodata shards build-planning#240)

Acceptance Criteria

• sharded repodata is enabled for conda and rattler-build RAPIDS-wide

Approach

Revert #564

Notes

N/A