environment: migrate apply_default_whitespace and apply_default_ignorewhitespace

environment: migrate apply_default_whitespace and apply_default_ignorewhitespace

The global variables 'apply_default_whitespace' and
'apply_default_ignorewhitespace' are used to store the default
whitespace configuration for 'git apply'. Move these variables
into 'struct repo_config_values' to continue the libification
effort.

Dynamically allocated strings fetched via 'repo_config_get_string()'
are now tracked per-repository and safely freed in
'repo_config_values_clear()'.

As part of this transition, update 'git_apply_config()' to accept a
'struct repository *' argument rather than relying on the
'the_repository' global.

Mentored-by: Christian Couder <redacted>
Mentored-by: Ayush Chandekar <redacted>
Mentored-by: Olamide Caleb Bello <redacted>
Signed-off-by: Tian Yuchen <redacted>
Signed-off-by: Junio C Hamano <redacted>