update email regex

[Prabalpsingh7115]

Overview

1. This PR does the following
   a- The regex filter for institute email id was only checking for the substring "@iiitdmj.ac.in" which is now replaced and
   checking if the email id is ending with the above substring.
   b- Fixed a bug where user can go to Signin and Signup page by url even if he/she is logged in.
   c- Added a validation for phone number.

Essential Checklist

• The PR title starts with "Fix #bugnum: ", followed by a short, clear summary of the changes. (If this PR fixes part of an issue, prefix the title with "Fix part of #bugnum: ...".)
• "Allow edits from maintainers" is checked. (See here for instructions on how to enable it.)
• The PR is made from a branch that's not called "main/master".

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[Priyansh61]

@Prabalpsingh7115 kindly update the PR description?

[Priyansh61]

@Prabalpsingh7115 Please update the PR

[Prabalpsingh7115]

@Priyansh61 I have updated the description. Kindly review the PR .