feat(axum-conversion): ported `/login` and `/signup` to axum

[LukeBrandon]

Description of changes:

• [x] Added signup route to axum api
  • POST /users/signup
• [x] Added login route to axum api
  • GET /users/login
• Removed old backend/ crate
• Renamed backend-axum/ to backend/

Misc other changes:

• Updated workflow for build
• Checked in sqlx-data.json to fix offline cargo build with sqlx macros
  • See: https://github.com/launchbadge/sqlx/blob/main/sqlx-cli/README.md#enable-building-in-offline-mode-with-query
  • This is still not working but it is closer.

[FlynnOConnell]

One day this build wont fail