new linter: do not use db_column in model fields

[atodorov]

db_column argument in model field definitions is a legacy leftover and in many cases the column name in the DB is a bit different from the model field name. All of this has been fixed but it took lots of effort to do so.

Kiwi TCMS needs a custom kiwi_lint/ checker which will discover all of these issues (if we forgot to fix some) and prevent them from happening again.

Definition of Done:

• new checker class under kiwi_lint/ which implements the necessary pylint machinery
• Can be relatively simple checker b/c the db_column parameter name is rather unique and we probably don't use it for anything not related to declaring Django models. It should be sufficient to raise a warning when a function call contains a parameter with the name db_column.
• All code review passed & PR merged

Here's me explaining how to write pylint plugins:

• https://www.youtube.com/watch?v=3CkSKUNMLJc
• https://www.youtube.com/watch?v=D1wLFyazTRM

This issue is part of Kiwi TCMS open source bounty program. For more information see the link(s) in bounty-program milestone

[brymut]

@atodorov submitted new expense on https://opencollective.com/kiwitcms/expenses/24577