docs: add text version of certificates tutorial

[edibotopic]

The ADSys documentation contains one tutorial currently.

It is only presented in video format, and generally there should be a text-based version of any tutorial that is included in our documentation.

This PR provides a text-based version of the video tutorial. It attempts to adhere closely to the video content while adding/subtracting as necessary for clarity.

Some minor rewording is also done to the main and tutorial index pages to improve clarity and consistency.

UDENG-3603

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.80%. Comparing base (f01a3ac) to head (1270c01).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1073   +/-   ##
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  Coverage   93.80%   93.80%           
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  Files          79       79           
  Lines        6881     6881           
=======================================
  Hits         6455     6455           
  Misses        416      416           
  Partials       10       10           

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[jibel]

Thanks for the transcription of the demo in a tutorial. Only request is to change the version of Ubuntu to the latest LTS

[edibotopic]

thanks @jibel -- I was trying to maintain consistency with the video but I think it's better to update, as you suggest. Will do.

[jibel]

All good!