Add prime checker

[skepttalk]

This PR adds a PrimeNumber.java program to the Java-Programs repository.

The program takes an integer input from the user and determines whether it is a prime number.
It introduces beginners to loops, conditional statements, and mathematical operations in Java.

[IamBisrutPyne]

Hey @skepttalk

These are great contributions to the Beginner folders.
As I have stated in the guidelines,

Please only submit one program per PR to maintain brevity and ensure mergeability for Hacktoberfest

As noted in your last PR, administrative files like CONTRIBUTING.md are centrally managed and procedurally-generated. Please remove the CONTRIBUTING.md file from this PR before we can review the code.
Also, the file is missing the required Javadocs-style header block (Title, Author, Date, Description, Time Complexity, and Space Complexity). (Note: This simple solution is $O(N)$ Time and $O(N)$ Space).