Tech stack: Go: add `Errors` section

[qdm12]

➡️ Rendered

Progress:

• [x] Errors introduction
• [x] Whether to export sentinel errors
• [x] Wrap or wrapped
• [x] Whether to add context
• [x] Concrete example
• [x] Testing errors
• [ ] Debated with the Gossamer team (others are welcome too)
• [ ] Improve concrete example code

[render[bot]]

Your Render PR Server URL is https://engineering-handbook-pr-62.onrender.com.

Follow its progress at https://dashboard.render.com/static/srv-cbqhsiirrk09aurqbu20.

[mpetrunic]

conflicts^^

[qdm12]

Please hold on merging this, I need to add the sentinel error definition :wink:

[qdm12]

Please hold on merging this, I'll review example code and improve it soon-ish.

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