chore: Fix missing baseUrl handling in JS and cover by testts

Problem/Motivation

Now we have many places where get the URL in JS directly from the browser. That works for common setups where Drupal is on the root path, but will not work on setups with the baseUrl not empty, like "http://example.com/my-site".

Steps to reproduce

Here are a couple of places where this should be fixed:
- https://git.drupalcode.org/issue/commercetools-3516884/-/blob/5125fb6924...
- https://git.drupalcode.org/issue/commercetools-3516884/-/blob/5125fb6924...

Proposed resolution

First of all, we need to understand why tests are passing with this issue, and make the tests check this issue and fail.
Then, fix the code to make the tests pass again.