🏗️(frontend) Footer configurable

To have different footer per instance the
content of the footer is now configurable
from the theme customization file.

See THEME_CUSTOMIZATION_FILE_PATH env var.

src/helm/env.d/dev/configuration/theme/demo.json

@@ -1,6 +1,12 @@
 {
   "footer": {
     "default": {
+      "logo": {
+        "src": "/assets/icon-docs.svg",
+        "width": "54px",
+        "alt": "Docs Logo",
+        "withTitle": true
+      },
       "externalLinks": [
         {
           "label": "Github",