Make OTPs truly random

# Problem
Currently, the 'Forgot password' activity uses a hardcoded OTP at [ForgotPassword.java](https://github.com/CSI-CATT-DMCE/Care4U/blob/main/app/src/main/java/com/example/innovathon2022_care4u/ForgotPassword.java#L23-L35).

## Potential fix
1. Generate a random OTP when the activity is created.
2. Compare this OTP with the one in the text field.

Open app/src/main/java/com/example/innovathon2022_care4u/ForgotPassword.java and inspect lines 23-35, where the hardcoded OTP is used. Trace the Forgot password activity's creation and text-field comparison, then verify the flow with multiple attempts. Done means each activity creation uses a random OTP and the entered value is compared against that OTP.

Written by the indexing model from the issue text.