The git_user_agent_sanitized() function performs some sanitizing to
avoid special characters being sent over the line and possibly messing
up with the protocol or with the parsing on the other side.

Let's extract this sanitizing into a new redact_non_printables() function,
as we will want to reuse it in a following patch.

For now the new redact_non_printables() function is still static as
it's only needed locally.

While at it, let's also make a few small improvements:
  - use 'size_t' for 'i' instead of 'int',
  - move the declaration of 'i' inside the 'for ( ... )',
  - use strbuf_detach() to explicitly detach the string contained by
    the 'buf' strbuf.

Mentored-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Usman Akinyemi <usmanakinyemi202@gmail.com>

Some code from "builtin/bugreport.c" uses uname(2) to get system
information.

Let's refactor this code into a new get_uname_info() function, so
that we can reuse it in a following commit.

Mentored-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Usman Akinyemi <usmanakinyemi202@gmail.com>

As some issues that can happen with a Git client can be operating system
specific, it can be useful for a server to know which OS a client is
using. In the same way it can be useful for a client to know which OS
a server is using.

Let's introduce a new protocol (`os-version`) allowing Git clients and
servers to exchange operating system information. The protocol is
controlled by the new `transfer.advertiseOSVersion` config option.

Add the `transfer.advertiseOSVersion` config option to address
privacy concerns issue. It defaults to `true` and can be changed to
`false`. When enabled, this option makes clients and servers send each
other the OS name (e.g., "Linux" or "Windows"). The information is
retrieved using the 'sysname' field of the `uname(2)` system call.

However, there are differences between `uname(1)` (command-line utility)
and `uname(2)` (system call) outputs on Windows. These discrepancies
complicate testing on Windows platforms. For example:
  - `uname(1)` output: MINGW64_NT-10.0-20348.3.4.10-87d57229.x86_64\
  .2024-02-14.20:17.UTC.x86_64
  - `uname(2)` output: Windows.10.0.20348

Until a good way to test the feature on Windows is found, the
transfer.advertiseOSVersion is set to false on Windows during testing.

Mentored-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Usman Akinyemi <usmanakinyemi202@gmail.com>