Pipeline Allowing Duplicate db_name Entries / Not Ensuring Unique Values

### Description of the bug James Fellows Yates suggests that the pipeline should undergo input validation to ensure that if multiple databases are used, they each have a unique db_name. However, right now the pipeline will allow a user to list the same db_name value for multiple databases which causes issues with downstream Krona visualization. Discussion of the issue: https://nfcore.slack.com/archives/C031QH57DSS/p1760563017457389 ### Command used and terminal output ```console ``` ### Relevant files > ### System information _No response_