Add a flag button in the segmentation GUI to flag cases

[maxradx]

Is your feature request related to a problem? Please describe.
Add a flag button to flag a case and save that the case has been flagged in the statistics file generated (e.g. metadata) could improve follow-up on specific cases.

Describe the solution you'd like
A toggle button where a case can be flagged and selected from the GUI in the segmentation.

Describe alternatives you've considered
Integrate the option in classification files.

Additional context
N/A.