Using 404 HTTP response code in username exist error

[ryumada]

https://github.com/REPfit-Retail-Price-Fit/backend-main/blob/45eb8fb5e6cd301e9b2521e37b49f6d3b4c8848c/docs/register/%5BPOST%5D%20Register%20a%20new%20account.md?plain=1#L46-L54

Maybe the HTTP response code is ambiguous. But I found a reference here: https://stackoverflow.com/questions/5604816/whats-the-most-appropriate-http-status-code-for-an-item-not-found-error-page.

bmargulies says we should not worry about any HTTP error code for handling errors. We can focus on giving the additional message instead. That's why I stick to using 404 Not Found.

Please consider to check it @akhfzz.

[ryumada]

Okay finally I realized the code is not 404 NOT FOUND, but we can use 409 CONFLICT. Please see this new discussion: #10 (comment)