environment: consolidate config values
The config values parsed in git_default_config() such as
core.attributesFile are loaded eagerly and stored in global variables.
Storing these values in global variables can lead to unexpected
behaviours when more than one Git repository run in the same Git process.
Move these values into a struct config_values which can be accessed per
repository. This centralization will be important in moving other
variables and this will prevent us from moving any code from
git_default_config(), ensuring the current behaviour remains the same
while also enabling the libification of Git.
Suggested-by: Phillip Wood phillip.wood123@gmail.com Signed-off-by: Olamide Caleb Bello belkid98@gmail.com