Merge branch 'ob/core-attributesfile-in-repository' into next

Merge branch 'ob/core-attributesfile-in-repository' into next

The core.attributesfile is intended to be set per repository, but
were kept track of by a single global variable in-core, which has
been corrected by moving it to per-repository data structure.

* ob/core-attributesfile-in-repository:
  environment: move "branch.autoSetupMerge" into `struct repo_config_values`
  environment: stop using core.sparseCheckout globally
  environment: stop storing `core.attributesFile` globally