gh-101536: [docs] Improve attributes of urllib.error.HTTPError (#101612)

* gh-101536: [docs] Improve attributes of `urllib.error.HTTPError`

* Address review

Author: sobolevn

Doc/library/urllib.error.rst

@@ -31,14 +31,19 @@ The following exceptions are raised by :mod:`urllib.error` as appropriate:
       of :exc:`IOError`.
 
 
-.. exception:: HTTPError
+.. exception:: HTTPError(url, code, msg, hdrs, fp)
 
    Though being an exception (a subclass of :exc:`URLError`), an
    :exc:`HTTPError` can also function as a non-exceptional file-like return
    value (the same thing that :func:`~urllib.request.urlopen` returns).  This
    is useful when handling exotic HTTP errors, such as requests for
    authentication.
 
+   .. attribute:: url
+
+      Contains the request URL.
+      An alias for *filename* attribute.
+
    .. attribute:: code
 
       An HTTP status code as defined in :rfc:`2616`.  This numeric value corresponds
@@ -48,14 +53,20 @@ The following exceptions are raised by :mod:`urllib.error` as appropriate:
    .. attribute:: reason
 
       This is usually a string explaining the reason for this error.
+      An alias for *msg* attribute.
 
    .. attribute:: headers
 
       The HTTP response headers for the HTTP request that caused the
       :exc:`HTTPError`.
+      An alias for *hdrs* attribute.
 
       .. versionadded:: 3.4
 
+   .. attribute:: fp
+
+      A file-like object where the HTTP error body can be read from.
+
 .. exception:: ContentTooShortError(msg, content)
 
    This exception is raised when the :func:`~urllib.request.urlretrieve`