environment: move autorebase into repo_config_values
The global variable 'autorebase' dictates whether a newly created branch should be configured to automatically rebase by default. Move it into 'struct repo_config_values' to continue the libification effort. The 'enum rebase_setup_type' definition is moved higher up in 'environment.h' so that it is visible to the repository-specific structure. The default state AUTOREBASE_NEVER is now correctly initialized in 'repo_config_values_init()'. Configuration parsing in 'git_default_branch_config()' is updated to write directly to the repository's configuration instance. Mentored-by: Christian Couder <christian.couder@gmail.com> Mentored-by: Ayush Chandekar <ayu.chandekar@gmail.com> Mentored-by: Olamide Caleb Bello <belkid98@gmail.com> Signed-off-by: Tian Yuchen <cat@malon.dev> Signed-off-by: Junio C Hamano <gitster@pobox.com>