Added email verification while creating user and sending email

[pc9795]

Description

Added email verification during User creation by adding Java validation API @Email annotation on the email field of the User object. Updated the email verification logic in the EmailSender using Apache commons validator's EmailValidator

Fixes #627

Type of change

• Bugfix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Locally using Postman

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented on my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[pc9795]

Right now we will get a generic message "Bad Request: Validation failure" while creating User from the API but after merging #1084 we will get a nicely formatted message specifically telling what is failed.

[pc9795]

FYI: @Nikhil-Nandagopal

[mohanarpit]

@pc9795 Thanks for this PR. Is it possible to write a test to assert the email validation is happening properly? Will ensure that in the future, if any other developer changes the validation, the tests can ensure that the change is valid.

[mohanarpit]

@pc9795 Thank you so much for this change! 👏