Use new Cody Auth site for authentication

[tjdevries]

This is a large PR, but not as large as the diff numbers give me credit for ;) ~230k of the lines are from updating cody (must be some new deps added to the bundle or something)

Checklist:

• Update to latest cody agent (might want to double check before merging though)
• Start localhost http server to redirect
• Handle the redirect live, probably should update user as well
• Open Cody PLG site
• Store secrets in secret store
• Retrieve secrets from secret store on startup
• Ensure all binaries are using same secrets
• Remove Cody App auth
• Remove "nvim" auth
• Remove old nvim auth storage
• Allow for SRC_* variables to still override
• Handle rate limits for Cody Free
• Handle rate limits for Cody Pro
• Don't spam rate limit messages
• Add checkhealth for auth status
• Add checkhealth for rate limit
• Update checkhealth messages for new auth
• Handle changing auth in nvim session
• Allow for sending notifications from sg-nvim-agent -> neovim