Add tests folder with sample test and instructions

[MarkoSagadin]

Description

This PR adds a tests folder with sample test project and instructions on how to run it.

Areas of interest for the reviewer

See added sample_test dir and README.md.

The purpose of this PR is to provide some starting point for writing unit tests.

Please see if this could be better.

Checklist

• [x] My code follows the [style guidelines] as defined by IRNAS.
• [x] I have performed a self-review of my code.
• [x] My changes generate no new warnings.
• [x] I added/updated source code documentation for all newly added or changed functions.
• [x] I updated all customer-facing technical documentation. - This PR introduced only internal facing changes.

After-review steps

• I will merge PR by myself.

[style guidelines]: https://github.com/IRNAS/irnas-guidelines-docs/blob/main/docs/developer_guidelines.md

[MarkoSagadin]

Current dependencies on/for this PR:

• main
  • PR #6 👈

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[MarkoSagadin]

@TjazVracko I have just force-pushed changes, check my replies above. Also check if the change in the CMakelists.txt is ok.