remote: introduce remote.<name>.serverOption configuration

Currently, server options for Git protocol v2 can only be specified via
the command line option "--server-option" or "-o", which is inconvenient
when users want to specify a list of default options to send. Therefore,
we are introducing a new configuration to hold a list of default server
options, akin to the `push.pushOption` configuration for push options.

Initially, I named the new configuration `fetch.serverOption` to align
with `push.pushOption`. However, after discussing with Patrick, it was
renamed to `remote.<name>.serverOption` as suggested, because:

1. Server options are designed to be server-specific, making it more
   logical to use a per-remote configuration.
2. Using "fetch." prefixed configurations in git-clone or git-ls-remote
   seems out of place and inconsistent in design.

The parsing logic for `remote.<name>.serverOption` also relies on
`transport.c:parse_transport_option`, similar to `push.pushOption`, and
they follow the same priority design:

1. Server options set in lower-priority configuration files (e.g.,
   /etc/gitconfig or $HOME/.gitconfig) can be overridden or unset in
   more specific repository configurations using an empty string.
2. Command-line specified server options take precedence over those from
   the configuration.

Server options from configuration are stored to the corresponding
`remote.h:remote` as a new field `server_options`.  The field will be
utilized in the subsequent commit to help initialize the
`server_options` of `transport.h:transport`.

And documentation have been updated accordingly.

Helped-by: Patrick Steinhardt <ps@pks.im>
Helped-by: Junio C Hamano <gitster@pobox.com>
Reported-by: Liu Zhongbo <liuzhongbo.6666@bytedance.com>
Signed-off-by: Xing Xin <xingxin.xx@bytedance.com>
Reviewed-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

remote.h

@@ -4,6 +4,7 @@
 #include "hash.h"
 #include "hashmap.h"
 #include "refspec.h"
+#include "string-list.h"
 #include "strvec.h"
 
 struct option;
@@ -104,6 +105,8 @@ struct remote {
 
 	/* The method used for authenticating against `http_proxy`. */
 	char *http_proxy_authmethod;
+
+	struct string_list server_options;
 };
 
 /**