To Add Note Section in Matcher (#19260)

* refer #18633 and discussion with @rojkov on this issue adding Note Section here for better clarity for users on max_program_size

Signed-off-by: Abhay Narayan Katare <abhay.katare@india.nec.com>

Mirrored from https://github.com/envoyproxy/envoy @ 1c1e81217ca5ff5a59eb4384a9cc17f35f73d09f

envoy/type/matcher/v3/regex.proto

@@ -45,6 +45,12 @@ message RegexMatcher {
     //
     // This field is deprecated; regexp validation should be performed on the management server
     // instead of being done by each individual client.
+    //
+    // .. note::
+    //
+    //  Although this field is deprecated, the program size will still be checked against the
+    //  global ``re2.max_program_size.error_level`` runtime value.
+    //
     google.protobuf.UInt32Value max_program_size = 1
         [deprecated = true, (envoy.annotations.deprecated_at_minor_version) = "3.0"];
   }