Add hyphen as an allowed char for properties

[CharlesNepote]

The file to modify is: https://github.com/openfoodfacts/folksonomy_api/blob/main/folksonomy/models.py
Just modify:

• re_key = re.compile(r'[a-z0-9_]+(\:[a-z0-9_]+)*')
• and raise ValueError('k must be alpha-numeric [a-z0-9_:]')

And add tests into: https://github.com/openfoodfacts/folksonomy_api/blob/main/tests/test_main.py