Setup CI workflow

[sudotensor]

Currently, there is no CI workflow setup to make sure that both examples, MCUBoot and Mock, build successfully on each push to the repository. The aim is to setup a GitHub actions workflow that uses the new CLI build tool fota.sh (from branch build-process-automation) to build the examples and check for any errors; known errors (documented in #1) are ignored or have workarounds implemented to avoid them.

Note: It is not a strict requirement to run the examples on the target board using the CI workflow by means of a Raspberry Pi rig connected to an NRF52840_DK target board. Support for this can be added later considering that the new build tool supports building the examples without providing a mount point.

Requirements:

• Setup basic actions workflow
• Add build step for Mock example
• Add build step for MCUboot example

Associated branch: ci-setup