Handle loading spinner on API calls

**What it's the actual situation on ARA ?**
The loading spinner is manually managed by using a (boolean) variable to show/hide it depending on its current state (e.g. waiting for the API call to finish, errors, etc.). Although this works, there are a few disadvantages:
- This is extra work
- It can be error prone (e.g. forgetting to end the spinner)
- You can forget to add it
- It is not a good practice

**Describe the solution you'd like**
An interceptor is a good solution.

> **IMPORTANT**: Don't forget to delete all the "manual" spinners

Start by tracing the API-call paths that manually toggle the loading spinner and identify the request entry point where interceptor-based handling belongs. Done means spinner handling is centralized and all manual spinner management is removed; verify the affected API-call flows, including errors.

Written by the indexing model from the issue text.