Adding error handling with toast component!

[mdefend]

Added error handling with toast that gives a message to the user for an invalid guest code and already taken username.

[foleyash]

Hi Maggie, looks great and works as expected! If you could remove any debugging console.log()'s inside of 'src/app/page.tsx' and 'src/app/api/sessionDB/connect/route.ts' to keep the source code more concise before I pull these changes that would be great.

Also, I was thinking we could also do the following just to improve user experience even more (if you are interested):

• When the user attempts to log in with a duplicate username, clear the username input and focus its form input element (look into the focus() method in javascript)
• When the user attempts to join a session with an invalid guest code, clear the guest code input and focus its form input element (same as above)