has_played_20_games should be renamed

[glbert-does]

heltour/heltour/tournament/models.py

Line 1762 in 15dce1b

has_played_20_games = models.BooleanField()

has_played_20_games is a name that has been incorrect for 7 or 8 years – nowadays it should be has_established_rating or something similar.
this is a very small thing, but i still think it should be renamed. it's confusing if you're not familiar with how rating deviation worked on lichess historically and/or how the league rules changed to reflect this. mostly adding this issue so we don't forget about it.