Add Postman tests to pipeline

[Brend-Smits]

Is your feature request related to a problem? Please describe.
Postman tests exist, but are not yet executed when a pull request is created

Describe the solution you'd like
Add the postman tests to the pipeline and trigger them on pull request

Additional context
Postman files can be found in /Postman directory.

[RensvdLinden]

I will work on this during the holiday

[Brend-Smits]

Postman Tests should be executed in the pipeline; we need to set up a temporary backend in Github Actions, then the postman tests (which will also be executed in the same Github Actions environment) can use "localhost" to communicate with the backend.
A separate environment will need to be created in Postman to accommodate this change.

[matir8]

There's an issue with the certificates set up on the development docker environment. The same problem as #200. The API and the Identity server can't establish HTTPS connection which leads to an authentication error.