feat: gzip js, css, SVG icons assets (#11208)

As pointed by @github-throwaway in
openfoodfacts/smooth-app#5583 (comment)
, we currently serve uncompressed assets (CSS, JS etc.).

We should add .gz versions so that they can be served by nginx. We need
to keep the non .gz files as well as we use try_files, which returns a
404 if the uncompressed file does not exist:

```
                try_files resources/$uri $uri $uri/ =404;
                gzip_static always;
                gunzip on;
```

gulpfile.ts

@@ -3,6 +3,7 @@ import { init, write } from "gulp-sourcemaps";
 
 import concat from "gulp-concat";
 import gulpSass from "gulp-sass";
+import gzip from "gulp-gzip";
 import minifyCSS from "gulp-csso";
 import sassLib from "sass";
 import svgmin from "gulp-svgmin";
@@ -23,27 +24,41 @@ const sassSrc = "./scss/**/*.scss";
 
 const imagesSrc = ["./node_modules/leaflet/dist/**/*.png"];
 
+// nginx needs both uncompressed and compressed files as we use try_files with gzip_static always & gunzip
+
 export function icons() {
-  return src("*.svg", { cwd: "./icons" }).
+  const processed = src("*.svg", { cwd: "./icons" }).
     pipe(
       svgmin({
         // @ts-ignore
         configFile: "icons/svgo.config.js",
       })
     ).
     pipe(dest("./html/images/icons/dist"));
+
+  const compressed = processed.
+    pipe(gzip()).
+    pipe(dest("./html/images/icons/dist"));
+
+  return processed && compressed;
 }
 
 export function attributesIcons() {
-  return src("*.svg", { cwd: "./html/images/attributes/src" }).
+  const processed = src("*.svg", { cwd: "./html/images/attributes/src" }).
     pipe(svgmin()).
     pipe(dest("./html/images/attributes/dist"));
+
+  const compressed = processed.
+    pipe(gzip()).
+    pipe(dest("./html/images/attributes/dist"));
+
+  return processed && compressed;
 }
 
 export function css() {
   console.log("(re)building css");
 
-  return src(sassSrc).
+  const processed = src(sassSrc).
     pipe(init()).
     pipe(
       sass({
@@ -55,10 +70,16 @@ export function css() {
     pipe(minifyCSS()).
     pipe(write(".")).
     pipe(dest("./html/css/dist"));
+
+  const compressed = processed.
+    pipe(gzip()).
+    pipe(dest("./html/css/dist"));
+
+  return processed && compressed;
 }
 
 export function copyJs() {
-  return src([
+  const processed = src([
     "./node_modules/@webcomponents/**/webcomponentsjs/**/*.js",
     "./node_modules/foundation-sites/js/vendor/*.js",
     "./node_modules/foundation-sites/js/foundation.js",
@@ -84,20 +105,32 @@ export function copyJs() {
     pipe(terser()).
     pipe(write(".")).
     pipe(dest("./html/js/dist"));
+
+  const compressed = processed.
+    pipe(gzip()).
+    pipe(dest("./html/js/dist"));
+
+  return processed && compressed;
 }
 
 export function buildJs() {
   console.log("(re)building js");
 
-  return src(jsSrc).
+  const processed = src(jsSrc).
     pipe(init()).
     pipe(terser()).
     pipe(write(".")).
     pipe(dest("./html/js/dist"));
+
+  const compressed = processed.
+    pipe(gzip()).
+    pipe(dest("./html/js/dist"));
+
+  return processed && compressed;
 }
 
 function buildjQueryUi() {
-  return src([
+  const processed = src([
     "./node_modules/jquery-ui/ui/jquery-patch.js",
     "./node_modules/jquery-ui/ui/version.js",
     "./node_modules/jquery-ui/ui/widget.js",
@@ -113,10 +146,16 @@ function buildjQueryUi() {
     pipe(concat("jquery-ui.js")).
     pipe(write(".")).
     pipe(dest("./html/js/dist"));
+
+  const compressed = processed.
+    pipe(gzip()).
+    pipe(dest("./html/js/dist"));
+
+  return processed && compressed;
 }
 
 function jQueryUiThemes() {
-  return src([
+  const processed = src([
     "./node_modules/jquery-ui/themes/base/core.css",
     "./node_modules/jquery-ui/themes/base/autocomplete.css",
     "./node_modules/jquery-ui/themes/base/menu.css",
@@ -127,10 +166,16 @@ function jQueryUiThemes() {
     pipe(concat("jquery-ui.css")).
     pipe(write(".")).
     pipe(dest("./html/css/dist/jqueryui/themes/base"));
+
+  const compressed = processed.
+    pipe(gzip()).
+    pipe(dest("./html/css/dist/jqueryui/themes/base"));
+
+  return processed && compressed;
 }
 
 function copyCss() {
-  return src([
+  const processed = src([
     "./node_modules/leaflet/dist/leaflet.css",
     "./node_modules/leaflet.markercluster/dist/MarkerCluster.css",
     "./node_modules/leaflet.markercluster/dist/MarkerCluster.Default.css",
@@ -142,6 +187,12 @@ function copyCss() {
     pipe(minifyCSS()).
     pipe(write(".")).
     pipe(dest("./html/css/dist"));
+
+  const compressed = processed.
+    pipe(gzip()).
+    pipe(dest("./html/css/dist"));
+
+  return processed && compressed;
 }
 
 function copyImages() {