[context] Support config file option "proxy_auth_method", defaults "any"
[context] Support config file option "proxy_auth_method", defaults "any"

Adds support for the "proxy_auth_method" configuration file option.
The default value is set to "any". Before that, the default
librepo/libcurl value "basic" was used.

Related to https://bugzilla.redhat.com/show_bug.cgi?id=1924001 .

rpm-software-management/libdnf,rpm-software-management/libdnf,rpm-software-management/libdnf,rpm-software-management/libdnf