Add example for dhara (IEC-198)

[anastasia-be]

[igrr]

Currently dhara component is tested by spi_nand_flash component examples/tests.

Since dhara "port layer" is inside "spi_nand_flash", it's a bit difficult to write an example for dhara in isolation. We probably need to refactor spi_nand_flash to make this possible.

[anastasia-be]

@igrr thank you for your feedback!

Let’s coordinate on finalizing the plan for this work and I will set a task for refactor of the spi_nand_flash to separate out the dhara component.