Change field length of civicrm_option_value.label from 255 to 512

There might be several cases, where the length of this field might not be long enough.

One relevant use case regards to internationalization, especially for postal and email greetings: As described here, this database field is used for smarty code, that populates the greeting fields with different values, whether communication_style is formal or familiar, or if the contact is female or male. This is relevant for many languages like spanish, german, italian.

E.g.: "Sehr geehrte Frau Dr. Müller" versus "Sehr geehrte*r* Herr Meier":

The entries for postal_greeting and email_greeting are stored in civicrm_option_value.label
As we know by now, for many organizations the currently available 255 characters are not enough to store the necessary smarty syntax.

We could simply change the database by ALTER TABLE CHANGE COLUMN for each CiviCRM install. However, we don't want that quick and dirty approach, that also might create trouble with upgrade scripts.