Added password validator on the login screen.

[Mehul-Kumar-27]

Description

Added the password validator at the login screen for convince of the user. The validations are same as that used in the signup screen.

Fixes #223

Type of change

Please delete options that are not relevant.

• [ ] Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] Any dependent changes have been merged and published in downstream modules
• [x] I have checked my code and corrected any misspellings

Maintainer Checklist

• [ ] closes #xxxx (Replace xxxx with the GitHub issue number)
• [ ] Tag the PR with the appropriate labels