zephyr: add system tests to native_sim

[casaroli]

Narrative

As the Ocre developer, I want to run the System Tests in a Zephyr native_sim on every PR so I can be sure nothing broke the Zephyr functionality

Since there is no concept of multiple applications in Zephyr, we are left with the only option of creating 4 different apps for the system test groups.

Unlike POSIX, which we can build all the apps in one go, in Zephyr they must be separate apps.

TODO

• Investigate the tests/system/posix/ build
  • Note that there are 4 different applications built there
• For app in test applications:
  • Create directory tests/system/zephyr/*
  • add board files for native_sim
  • add Zephyr CMakeLists.txt to build zephyr app
  • add prj.cnf and whatever is necessary for the Zephyr application to build out of the box
• Do not modify any files matching tests/system/*.c
• Add the execution of all tests to the CI (KISS)

Out of scope (do not do)

• Merge the 4 test groups into a single application: we will investigate this in the future
• Edit any .c files: ideally we do not need to change any source files for this to work

[kr-t]

Similar/same tests can be created/run on U585 board as well at @PatrickRobbIOL

[kr-t]

I think this issue shall be prioritized, this is important to get right.