minor #14995 [HttpClient] Fix specifying http_version in YAML (pableu)

This PR was submitted for the 5.2 branch but it was merged into the 4.4 branch instead.

Discussion
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[HttpClient] Fix specifying http_version in YAML

With the code from the docs, I get this exception:

> Unrecognized option "http_version" under "framework.http_client". Available options are "default_options", "enabled", "max_host_connections", "mock_response_factory", "scoped_clients".

Maybe the XML and PHP Annotation also needs a fix, but I don't feel confident doing that.

Commits
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7948311 fix specifying http_version in YAML

Author: javiereguiluz

http_client.rst

@@ -750,7 +750,8 @@ the ``http_version`` option:
         # config/packages/framework.yaml
         framework:
             http_client:
-                http_version: '2.0'
+                default_options:
+                    http_version: '2.0'
 
     .. code-block:: xml