devpi-server: wrap package with plugins

Introduces `extraPackages` argument so optional plugins (and additional
packages can be utilized by devpi-server).

pkgs/by-name/de/devpi-server/package.nix

@@ -1,4 +1,27 @@
-{ python3Packages }:
+{
+  lib,
+  python3,
+  runCommand,
+  # configurable options
+  extraPackages ? (ps: [ ]),
+}:
 
-with python3Packages;
-toPythonApplication devpi-server
+let
+  pythonEnv = python3.withPackages (ps: [ ps.devpi-server ] ++ extraPackages ps);
+  server = python3.pkgs.devpi-server;
+in
+runCommand "devpi-${server.version}"
+  {
+    inherit (server)
+      pname
+      version
+      meta
+      passthru
+      ;
+  }
+  ''
+    mkdir -p $out/bin
+    for bin in ${lib.getBin server}/bin/*; do
+      ln -s ${pythonEnv}/bin/$(basename "$bin") $out/bin/
+    done
+  ''