[5.0.x] Added stub release notes for 5.0.4.

Backport of 337e37f3bb7bc2fe4f2bcfc5f9586e4f36da72e3 from main

docs/releases/5.0.4.txt

@@ -0,0 +1,12 @@
+==========================
+Django 5.0.4 release notes
+==========================
+
+*Expected April 2, 2024*
+
+Django 5.0.4 fixes several bugs in 5.0.3.
+
+Bugfixes
+========
+
+* ...

docs/releases/index.txt

@@ -25,6 +25,7 @@ versions of the documentation contain the release notes for any later releases.
 .. toctree::
    :maxdepth: 1
 
+   5.0.4
    5.0.3
    5.0.2
    5.0.1