chore: store npm cache on host (#110)

# Ticket 🎫

This is part of dot-base/deployments#184

# Description 📖
Changes the npm cache location in the dev-overlay, so that the cache is
stored on the docker host.

.gitignore

@@ -1,4 +1,8 @@
+# macOS
 .DS_Store
+
+# npm
+.npm_cache
 node_modules
 build
 /dist

dev-overlay.yml

@@ -6,7 +6,8 @@ services:
     user: ${USERID}
     working_dir: /var/workspace
     environment:
-            HOME: "/tmp" # This is needed so npm can create the cache at the default location ~/.npm
+      # default npm cache location (~/.npm) is not writeable in the container
+      npm_config_cache: /var/workspace/.npm_cache
     volumes:
       - ${DEV_OVERLAY_DIR}:/var/workspace/:cached
     ports: