Contributor type as string rather than boolean

At the moment contributor type is signal;led by a boolean (is_individual = true / false). It would be more useful to turn this into a string with pre-specified values, or evenm an integer
1: Individual
2: Organisation
3: Group
4. Government agency
But this would require rippling through the entire system

The issue names the is_individual field but no files, tests, or entry points. Start by locating every use of is_individual, then determine the allowed contributor values and the migration scope; done means the chosen representation works consistently throughout the system.

Vom Indexierungsmodell aus dem Issue-Text verfasst.