docs: rename COREDUMP_PACKAGE_METADATA → ELF_PACKAGE_METADATA

The format described by this document is used not only for coredumps,
but also for other purposes, so we've outgrown the old title.

A redirect was added based on https://codepo8.github.io/github-redirection-demo/.
I tried to use a relative link, but it's hard to test if it works
before merging.

Co-authored-by: Benjamin Franzke <benjaminfranzke@googlemail.com>

docs/_layouts/forward.html

@@ -0,0 +1,14 @@
+<html lang="en">
+  <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
+  <head>
+    <meta http-equiv="refresh" content="0;url={{ page.target }}"/>
+    <link rel="canonical" href="{{ page.target }}"/>
+    <title>Redirecting to {{ page.target }}</title>
+  </head>
+  <body>
+    <p>
+      This document has moved.<br>
+      Redirecting to <a href="{{ page.target }}">{{ page.target }}</a>.
+    </p>
+  </body>
+</html>