Add max length of column

[Pierlou]

[Maybe not : CHARACTER VARYING instead] Useful for SQL uploads later on, to set the VARCHAR max length (ould use TEXT but impossible to set an index on a TEXT column) Could be in the profile section : {'tops': [ {'count': 2772, 'value': 'TTTTTTTT'}, {'count': 780, 'value': 'XXXXXXXXXX'}}], 'nb_distinct': 10, 'nb_missing_values': 28, 'max_length': 12}