nixos/archiver-appliance: purify Tomcat on start

Needed because webapps are extracted into their own directories,
and when the .war files are upgraded, the extracted directories aren't,
which makes Tomcat start the old Archiver Appliance.

This also would purge old unused libraries, which is a good thing.

Author: minijackson

nixos/modules/archiver-appliance.nix

@@ -284,6 +284,12 @@ in {
     services.tomcat = {
       enable = true;
 
+      # Needed to purge old configurations on upgrades,
+      # such as old `commonLibs`
+      # and also `webapps` which are extracted,
+      # but wouldn't change when updated.
+      purifyOnStart = true;
+
       webapps = [cfg.package];
 
       extraConfigFiles = [