ci: [NGOv1.X] Corrections of CI setup issues

[michalChrobot]

This PR focuses on fixing CI issues raised in #3303 and before. Specifically:

1. 2023.3 editor was removed from supported list since based on official info it transitioned into 6000 editor and 2023 editor (by itself) is not supported. The associated ticket was (MTT-11355)
2. In case of ubuntu and 2021 editor (MTT-11354) correct version of libssl is being installed
3. UTR command was corrected to use preinstalled UTR on the image instead of downloading it
4. Removed upm-ci project pack definition and converted Code Coverage test to use upm-pvp pack job
5. Simplifies some unnecessary CI commands
6. Added detailed comments regarding CI setup and commands
7. Created CI_README file which describes overall configuration structure.
8. For macOS devices we now use M1 model (Apple Silicon) in contrast to default x64 Intel Mac which introduced a lot of bit-flipping errors

[EmandM]

This looks fantastic! Just a final point. If you name the markdown file README.md rather than CI_README.md, github will show the README when you view the folder.

[michalChrobot]

Hey @EmandM @NoelStephensUnity, can I get your approval on this PR 😁? It's corresponding to #3329 so you can check/approve both and then I can proceed