docs: update docs and annotation of json formatter (#38484)

Commit Message: docs: update docs and annotation of json formatter
Additional Description:
Risk Level: low.
Testing: n/a.
Docs Changes:
Release Notes:
Platform Specific Features:
[Optional Runtime guard:]
[Optional Fixes #Issue]
[Optional Fixes commit #PR or SHA]
[Optional Deprecated:]
[Optional [API
Considerations](https://github.com/envoyproxy/envoy/blob/main/api/review_checklist.md):]

---------

Signed-off-by: wangbaiping(wbpcode) <wangbaiping@bytedance.com>
Signed-off-by: code <wbphub@gmail.com>
Co-authored-by: wangbaiping(wbpcode) <wangbaiping@bytedance.com>
Co-authored-by: phlax <phlax@users.noreply.github.com>

api/envoy/config/core/v3/substitution_format_string.proto

@@ -22,7 +22,12 @@ option (udpa.annotations.file_status).package_version_status = ACTIVE;
 // Optional configuration options to be used with json_format.
 message JsonFormatOptions {
   // The output JSON string properties will be sorted.
-  bool sort_properties = 1;
+  //
+  // .. note::
+  //   As the properties are always sorted, this option has no effect and is deprecated.
+  //
+  bool sort_properties = 1
+      [deprecated = true, (envoy.annotations.deprecated_at_minor_version) = "3.0"];
 }
 
 // Configuration to use multiple :ref:`command operators <config_access_log_command_operators>`
@@ -101,6 +106,12 @@ message SubstitutionFormatString {
   // * for ``text_format``, the output of the empty operator is changed from ``-`` to an
   //   empty string, so that empty values are omitted entirely.
   // * for ``json_format`` the keys with null values are omitted in the output structure.
+  //
+  // .. note::
+  //   This option does not work perfectly with ``json_format`` as keys with ``null`` values
+  //   will still be included in the output. See https://github.com/envoyproxy/envoy/issues/37941
+  //   for more details.
+  //
   bool omit_empty_values = 3;
 
   // Specify a ``content_type`` field.

test/integration/access_log_integration_test.cc

@@ -49,7 +49,6 @@ TEST_P(AccessLogIntegrationTest, ShouldReplaceInvalidUtf8) {
         v.set_string_value("%REQ(X-FORWARDED-FOR)%");
         auto fields = json->mutable_fields();
         (*fields)["x_forwarded_for"] = v;
-        log_format->mutable_json_format_options()->set_sort_properties(true);
         access_log_config_to_clobber->mutable_typed_config()->PackFrom(access_log_config);
       });
   testRouterDownstreamDisconnectBeforeRequestComplete();