docs: Add base pages for flank layers

[jan-goral]

Fixes #1509

This pull request adds documentation pages for the flank layers:

• architecture
  • presentation
    • cli
  • domain
  • data
  • adapter

Checklist

• Update mkdocs.yml

[github-actions]

CLA Assistant Lite bot All contributors have signed the CLA ✍️ ✅

[github-actions]

Timestamp: 2021-03-29 15:48:29
Buildscan url for ubuntu-workflow run 698390645

[jan-goral]

I have to figure out how to serve markdown files for mkdocs, from outside of docs directory. I cannot find it in documentation. Seems to mkdocs forces to use only the docs directory which is a ridiculous design decision. I have to make sure.

[Sloox]

Some changes :)