builtin/refs: add list subcommand

builtin/refs: add list subcommand

Git's reference management is distributed across multiple commands. As
part of an ongoing effort to consolidate and modernize reference
handling, introduce a `list` subcommand under the `git refs` umbrella as
a replacement for `git for-each-ref`.

Implement `cmd_refs_list` by having it call the `for_each_ref_core()`
helper function. This helper was factored out of the original
`cmd_for_each_ref` in a preceding commit, allowing both commands to
share the same core logic as independent peers.

Add documentation for the new command. The man page leverages the shared
options file, created in a previous commit, by using the AsciiDoc
`include::` macro to ensure consistency with git-for-each-ref(1).

Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: shejialuo <shejialuo@gmail.com>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Meet Soni <meetsoni3017@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>