whatsnew: cp273 codec (#10907797)

Also updated the docs and added the aliases mentioned by the
references.
diff --git a/Doc/library/codecs.rst b/Doc/library/codecs.rst
index 843de27..3729dac 100644
--- a/Doc/library/codecs.rst
+++ b/Doc/library/codecs.rst
@@ -971,6 +971,10 @@
 +-----------------+--------------------------------+--------------------------------+
 | cp037           | IBM037, IBM039                 | English                        |
 +-----------------+--------------------------------+--------------------------------+
+| cp273           | 273, IBM273, csIBM273          | German                         |
+|                 |                                |                                |
+|                 |                                | .. versionadded:: 3.4          |
++-----------------+--------------------------------+--------------------------------+
 | cp424           | EBCDIC-CP-HE, IBM424           | Hebrew                         |
 +-----------------+--------------------------------+--------------------------------+
 | cp437           | 437, IBM437                    | English                        |