release: Finish preparation for 4.15.0

.release.cfg

@@ -8,10 +8,13 b' done = true'
 done = true
 
 [task:fixes_on_stable]
+done = true
 
 [task:pip2nix_generated]
+done = true
 
 [task:changelog_updated]
+done = true
 
 [task:generate_api_docs]
 done = true
@@ -20,7 +23,7 b' done = true'
 done = true
 
 [release]
-state = in_progress
+state = prepared
 version = 4.15.0
 
 [task:generate_js_routes]