Feat: DevDocs Revamp

[rossgalloway]

The devdocs are currently in a state where they are functional and have lots of information on the multiple parts of Yearn, but this information is fragmented and sometimes outdated or inaccurate. The organizational structure is haphazard and reflects the piecemeal way that information has been added over the years. By consolidating, updating, and improving on the docs, there is an opportunity to fill a missing piece of Yearn's information ecosystem: The passive sales and marketing domain that is not captured with the dApp and out of scope of the social channels.

This PR is an effort to streamline and simplify the structure of the docs site so that is easy to use for Users, Developers, and DAO members/contributors.

• Original Document laying out goals: https://hackmd.io/@rossgalloway/rJgQN_5mR
• Slideshow showing progress and rationale for changes: https://docs.google.com/presentation/d/1rruTTqJMmg49LxhyvGHb80QgE4t_nXD_ZINr8yOhlLY/edit?usp=sharing

This PR is not expected to be approved like this as it is going to be hard to review everything. Instead I want to use it as an reference to discuss changes and particular sections and then push individual upgrades and updates to reach this point. There also need to be changes to the content of numerous section of the docs to maximize the impact of these changes and those updated will happen in the aforementioned individual upgrades.