Fixing common-utils fails when existing user’s primary group name differs from username

[sireeshajonnalagadda]

Description
Fixing #1514

Issue:
The common-utils feature was failing with groupadd: GID '100' already exists and usermod: UID '1000' already exists errors when trying to create users with GID 100 or modify existing users with conflicting UIDs.

Root Cause:
GID 100 is typically reserved for the users group in most Linux distributions
The script attempted to create new groups with existing GIDs without checking if they already exist
UID conflicts occurred when trying to modify users to UIDs already in use by other users

Changes Made:

1. Enhanced Group Name Detection (main.sh)
   Purpose: Properly detect existing group names for users instead of assuming the group name matches the username.
2. Added GID Conflict Handling
   Purpose: Use existing groups (like users with GID 100) instead of failing when trying to create them.
3. Added UID Conflict Prevention
   Purpose: Prevent UID conflicts by checking if the target UID is already in use by another user.
4. Added Test Scenario and Test Dockerfile
   Purpose: Test the specific case where GID 100 is requested to ensure the feature handles it gracefully.

Checklist:
Changes worked as expected.