nix: add shell.nix for CI builds

This currently doesn't work becuase of lack Qml and QtQuick:
```
test.qml:1 module "QtQuick" is not installed
```
https://github.com/NixOS/nixpkgs/issues/51990

Signed-off-by: Jakub Sokołowski <jakub@status.im>

ci/Jenkinsfile.linux

@@ -1,5 +1,5 @@
 #!/usr/bin/env groovy
-library 'status-jenkins-lib@v1.8.0'
+library 'status-jenkins-lib@linux-use-nix'
 
 /* Options section can't access functions in objects. */
 def isPRBuild = utils.isPRBuild()
@@ -72,21 +72,21 @@ pipeline {
 
   stages {
     stage('Deps') {
-      steps {
+      steps { script {
-        sh 'make update'
+        nix.shell('make update', pure: false)
-        sh 'make deps'
+        nix.shell('make deps', pure: false)
-      }
+      } }
     }
 
     stage('status-go') {
-      steps {
+      steps { script {
-        sh 'make status-go'
+        nix.shell('make status-go', pure: false)
-      }
+      } }
     }
 
     stage('Package') {
       steps { script {
-        linux.bundle('tgz-linux')
+        linux.bundle('tgz-linux', 1)
       } }
     }
 

nix.conf

@@ -0,0 +1,11 @@
+# NOTE: If you are in Asia you might want to add https://nix-cache-cn.status.im/ to extra-substituters
+extra-substituters = https://nix-cache.status.im/
+substituters = https://cache.nixos.org/
+trusted-public-keys = nix-cache.status.im-1:x/93lOfLU+duPplwMSBR+OlY4+mo+dCN7n0mr4oPwgY= cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
+# Some downloads are multiple GB, default is 5 minutes
+stalled-download-timeout = 3600
+connect-timeout = 10
+max-jobs = auto
+# Helps avoid removing currently used dependencies via garbage collection
+keep-derivations = true
+keep-outputs = true

shell.nix

@@ -0,0 +1,48 @@
+{
+  source ? builtins.fetchTarball {
+    url = "https://github.com/NixOS/nixpkgs/archive/c140730d40d723c3c74a8d24bceef363495a3aef.zip";
+    sha256 = "sha256:1bcms35idl4mggickf97z6sydyr8iyjjw93iahhzwczwc42dgs0b";
+  },
+  pkgs ? import (source) { }
+}:
+
+let
+  qtCustom = with pkgs.qt515; /* 5.15.8 */
+    env "qt-custom-${qtbase.version}" ([
+      qtbase
+      qtdeclarative
+      qtlottie
+      qtmultimedia
+      qtquickcontrols
+      qtquickcontrols2
+      qtsvg
+      qttools
+      qtwebengine
+    ]);
+in pkgs.mkShell {
+  name = "status-desktop-build-shell";
+
+  buildInputs = with pkgs; [
+    bash which curl wget git file unzip jq lsb-release
+    go cmake gnumake pkg-config gnugrep qtCustom
+    pcre nss pcsclite extra-cmake-modules
+    xorg.libxcb xorg.libX11 libxkbcommon
+  ] ++ (with gst_all_1; [
+    gst-libav gstreamer
+    gst-plugins-bad  gst-plugins-base
+    gst-plugins-good gst-plugins-ugly
+  ]);
+
+  # Avoid terminal issues.
+  TERM = "xterm";
+  LANG = "en_US.UTF-8";
+  LANGUAGE = "en_US.UTF-8";
+
+  QTDIR = qtCustom;
+  # https://github.com/NixOS/nixpkgs/pull/109649
+  QT_INSTALL_PLUGINS = "${qtCustom}/${pkgs.qt515.qtbase.qtPluginPrefix}";
+
+  shellHook = ''
+    export MAKEFLAGS="-j$NIX_BUILD_CORES"
+  '';
+}