* updated the test stage in the app Dockerfile

pipeline multiple updates

See merge request !4

pipeline multiple updates

See merge request !3

pipeline multiple updates

See merge request !2

* updated workflow rules
* updated job names
* updated container versions
* added a template for gke-initialization

* app's frontend and backend are combined and served together from Node.js

* add code block to demonstrate build process in a more readable way
  (other than the Makefile)
* emphasise the sensitivity of the JWT token

* NodeJS: v16
* NPM: v8
* Jest: v27
* Mongoose: v6

And fix some small issues along the way

APP_NODE_MODULE_DIRS contains two paths. Quoting that var breaks
the command and the node_module folders were not deleted.