environment: move "core.attributesfile" into repo-setting

When handling multiple repositories within the same process, relying on global state for accessing the "core.attributesfile" configuration can lead to incorrect values being used. It also makes it harder to isolate repositories and hinders the libification of git.

Move the "core.attributesfile" configuration into the struct repo_settings instead of relying on the global state. Add a new function repo_settings_get_attributesfile_path() to retrieve this setting in a repository-scoped manner

Reported-by: Ayush Chandekar ayu.chandekar@gmail.com Mentored-by: Christian Couder christian.couder@gmail.com Mentored-by: Usman Akinyemi usmanakinyemi202@gmail.com Signed-off-by: Olamide Caleb Bello belkid98@gmail.com