docs: new channel concept doc

[thulieblack]

Description

This PR adds the new channel spec term concept doc

Related issue(s)

Resolves #1006

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[github-actions[bot]]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	50
🟠 Accessibility	88
🟠 Best practices	83
🟢 SEO	90
🔴 PWA	30

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[derberg]

lgtm, but I see @fmvilas was reviewing, so better get 🟢 from him