Enable public-name conversion in create_report_grouped_stats()

[apulsipher]

This pull request adds support for generating public-facing disease reports by allowing the use of alternate, public-friendly disease names in the grouped statistics report. It introduces a new is.public parameter to the relevant functions, updates documentation, and adds tests to ensure correct behavior when public names are present or missing.

Support for public-facing disease names:

• Added an is.public parameter to create_report_grouped_stats and updated its usage in epitrax_report_grouped_stats, enabling the function to optionally use public-facing disease names if provided. [1] [2] [3]
• Modified the merging logic in create_report_grouped_stats to replace disease names with public-facing names when is.public is TRUE, and to warn if the required column is missing. The function also now removes the Public_name column from output.
• Updated documentation for create_report_grouped_stats to describe the new is.public parameter and its behavior. [1] [2]

Testing enhancements:

• Added tests to ensure correct behavior when generating reports with and without public-facing disease names, including cases where the Public_name column is missing.