Dev: Enhancement add support for dbGroup in is_unique and is_not_unique validation rules

[maniaba]

I recently posted a feature request on the CodeIgniter forum regarding the is_unique and is_not_unique validation rules. The current implementation lacks support for specifying a dbGroup, which can cause issues when working with multiple database connections.

Here is the forum post for additional context: https://forum.codeigniter.com/showthread.php?tid=91760

Request: I propose enhancing the is_unique and is_not_unique validation rules to optionally accept a dbGroup as a parameter. This would allow users to specify the database connection they want the rule to apply to, providing more flexibility in multi-database environments.

I am planning to submit a pull request (PR) with these changes soon. If there are any suggestions, please let me know.

Thank you for considering this enhancement!