minor symfony#21500 [HttpClient] Document new option auto_upgrade_http_version (ajgarlag)

This PR was squashed before being merged into the 7.4 branch.

Discussion
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[HttpClient] Document new option `auto_upgrade_http_version`

Fix symfony#21498

Commits
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ac1e0a2 [HttpClient] Document new option `auto_upgrade_http_version`

Author: javiereguiluz

http_client.rst

@@ -1789,6 +1789,17 @@ You can also pass a set of default options to your client thanks to the
 
     // ...
 
+.. _auto-upgrade-http-version:
+
+.. versionadded:: 7.4
+
+    Starting in Symfony 7.4, the option `auto_upgrade_http_version` can
+    be set to false to disable automatic HTTP protocol version upgrade when
+    desired.
+
+    The automatic HTTP version upgrade is always disabled for HTTP/1.0 requests,
+    regardless of the option value.
+
 HTTPlug
 ~~~~~~~
 
@@ -1890,6 +1901,9 @@ You can also pass a set of default options to your client thanks to the
 
     // ...
 
+
+See :ref:`auto_upgrade_http_version <auto-upgrade-http-version>` option for details about how the HTTP protocol version selection works.
+
 Native PHP Streams
 ~~~~~~~~~~~~~~~~~~