Maintenance: Add Debian 11 support to packager.io processes

.pkgr.yml

@@ -56,6 +56,18 @@ targets:
       - libimlib2
       - libimlib2-dev
       - shared-mime-info
+  debian-11:
+    dependencies:
+      - curl
+      - elasticsearch|elasticsearch-oss
+      - nginx|apache2
+      - postgresql|mariadb-server
+      - libimlib2
+      - shared-mime-info
+    build_dependencies:
+      - libimlib2
+      - libimlib2-dev
+      - shared-mime-info
   ubuntu-16.04:
     dependencies:
       - curl