use lib.makeScope and files to organize packages

Some of the improvements here include:

* rocksdb can actually use jemalloc now instead of just pulling in a
  second rocksdb for no reason
* "complement-runtime" factored back out into shell file
* complement image no longer uses `mkDerivation` for `copyToRoot`
  because that's what `buildEnv` is for
* complement image no longer sets `SERVER_NAME`, complement already does
  that
* all packages were factored out into `callPackage`-able files for use
  with a custom `lib.makeScope pkgs.newScope`
* new version of `mkPackage` has options that are easier to use and
  override such as `features`

nix/pkgs/oci-image/default.nix

@@ -0,0 +1,28 @@
+{ inputs
+
+# Dependencies
+, dockerTools
+, lib
+, main
+, stdenv
+, tini
+}:
+
+dockerTools.buildLayeredImage {
+  name = main.pname;
+  tag = "main";
+  created = "@${toString inputs.self.lastModified}";
+  contents = [
+    dockerTools.caCertificates
+  ];
+  config = {
+    Entrypoint = if !stdenv.isDarwin
+      # Use the `tini` init system so that signals (e.g. ctrl+c/SIGINT)
+      # are handled as expected
+      then [ "${lib.getExe' tini "tini"}" "--" ]
+      else [];
+    Cmd = [
+      "${lib.getExe main}"
+    ];
+  };
+}