feat: adding express error handling tiny bank API workshop

[Ksound22]

Checklist:

• I have read freeCodeCamp's contribution guidelines.
• My pull request has a descriptive title (not a vague title like Update index.md)

Closes #996

[ShaunSHamilton]

This looks good to me, but I do have suggestions:

1. It is easier to test functions than variables
   • Prefer function x() {} over const x = () => {}
   • The reason is because of hoisting and AST locs
2. Split the project up into modular pieces
   • Easier to test when a file just contains a few code blocks

I take it the lesson plan is?:
a) Teach error handling with try...catch
b) Then refactor to catch all thrown Errors with the middleware