Move all HTTP proxy agent related modules to a monorepo

[TooTallNate]

Converts this repository into a monorepo, containing the following npm packages:

• agent-base
• data-uri-to-buffer
• degenerator
• get-uri
• https-proxy-agent
• http-proxy-agent
• pac-proxy-agent
• pac-resolver
• proxy
• proxy-agent
• socks-proxy-agent

Why? Mainly for ease of maintenance. It's difficult to monitor 10+ repositories and keep their configurations in sync. Additionally:

• Uses Turborepo
• All packages have been converted to TypeScript
• Common issue tracker for all related packages
• Common eslint configuration
• Shared GH Actions setup
• Test changes for sub-packages against dependent parent packages