refactor: return custom error from utils when bcrypt fails

[mantariksh]

Problem

1. In src/app/utils/hash, we have utility functions which wrap calls to bcrypt.hash and bcrypt.compare in ResultAsync. However, we return a generic ApplicationError when these functions fail. This means that downstream functionality has to deal with the error as a generic ApplicationError without context of where it came from, e.g. when deciding what status code and message to return in mapRouteError. Developers have to search through all the service functions called in controllers one by one until they find where the ApplicationError was returned.
2. We have a generateOtp utility, but all the times when we need to call it, we have to create not just the OTP but a hash of it as well. Since these two bits of functionality always come together, it makes sense to have a utility function which does both.

Part of #941

Solution

1. Return a new HashingError when bcrypt fails. This makes the origin of the error much clearer.
2. Create a generateOtpWithHash utility function, so we can call generateOtpWithHash().andThen... instead of const otp = generateOtp(); hashData(otp).andThen.... Note that verification.service was left out (it still calls generateOtp instead of generateOtpWithHash) as it will be addressed together with the rest of Convert verification service to use neverthrow #941.