application_logs: add bootstrap option to set log format (#27816)

add bootstrap option to set log format

Signed-off-by: ohadvano <ohadvano@gmail.com>

Mirrored from https://github.com/envoyproxy/envoy @ 08dd6fedf0c433c341e74e689194beb23540932c

envoy/config/bootstrap/v3/bootstrap.proto

@@ -110,6 +110,11 @@ message Bootstrap {
         // support all the format flags specified in the :option:`--log-format`
         // command line options section, except for the ``%v`` and ``%_`` flags.
         google.protobuf.Struct json_format = 1;
+
+        // Flush application log in a format defined by a string. The text format
+        // can support all the format flags specified in the :option:`--log-format`
+        // command line option section.
+        string text_format = 2;
       }
     }