Replace generic favicon with Layer5 logo

[hortison]

Current Behavior

See https://github.com/layer5io/academy-build/tree/master/public/favicons

Desired Behavior

See https://layer5.io/brand

Implementation

Use the "5" mark.

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Contributor Guide

• 🎨 Wireframes and designs for Layer5 site in Figma (open invite)

[suttonskate]

@Namanv0509, is this for you?