doc: interpret-trailers: use “metadata” in Name as well

We now since the previous commit introduce the format as “trailers metadata”. We can replace “structured information” with “metadata” in the “Name” section to be consistent. While “structured information” does emphasize that the data is not loosely structured, we also say that this command adds to or parses this format. I don’t think that we need to emphasize that it is structured since clearly there is some structure there. Both “metadata” and “structured information” can convey the same information. But “metadata” is shorter and easier to deploy since it’s just one word. Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name> Signed-off-by: Junio C Hamano <gitster@pobox.com>