doc: Add SW architecture diagram

[elsalahy]

Summary:

This adds a be lated SW architecture diagram that is useful in visualizing the system architecture and libraries. Relates to this docs issue.

Changes:

• Added SW architecture diagram.

Notes for Reviewers:

Please check the spelling, maybe something needs to be improved,

Release Notes: (optional)

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[johanstokking]

What's the coloring for?

I see loraawan twice (two "a") + Secure Elelement (-"le")

[elsalahy]

@johanstokking good catch, shitty mac keyboard, thanks. The colors don't represent anything, should I make the image more plain?

[johanstokking]

@johanstokking The colors don't represent anything, should I make the image more plain?

Either use them for something or don't use random colors because that may be misleading.

I see you have examples that are LoRaWAN based and others that aren't connectivity based at all. That could be a distinction between coloring.

[elsalahy]

@johanstokking I can improve it, do you find the application and libraries coloring misleading, or only the application layer?

[elsalahy]

@johanstokking I updated the design to take advantage of the libraries coloring scheme and efficiently described the used libraries in each boilerplate application.