Replace outdated Yearn logo asset on docs site

[rossgalloway]

Summary

Replace the old Yearn logo / branding asset currently used on the docs site with the updated version.

Motivation

The docs site still shows outdated branding in at least one visible Yearn products asset.

Proposed changes

• locate the updated logo/image asset already available
• replace the old branding on the docs site asset/page
• verify the outdated Yearn Products image is no longer served

Acceptance criteria

• the outdated logo/branding asset is removed from the docs site
• the updated logo/image is used in its place

Tracker

• To-do ID: T-009