posthog feat: Action steps refactor

Problem

We have ActionSteps as a separate model that is never used in any clever way.

It would be much simpler to have it all stored in the action itself as a json map. This would make it easier to load and reason on

[x] Adds a new steps_json to the model
[x] Maps steps to create a new class from the related fields or the stored json
[x] Moves all code over to use this new class
[x] Adds migration code
[x] Writes to both places, reading from the steps_json if it exists
[x] Removes properties that weren't referenced anymore such as name

👉 Stay up-to-date with PostHog coding conventions for a smoother review.

May 02 '24 10:05 benjackwhite

Your pull request is modifying functions with the following pre-existing issues:

📄 File: posthog/hogql/property.py

Function	Unhandled Issue
`property_to_expr`	TypeError: Property.init() missing 1 required positional argument: 'key' posthog.ta... `Event Count:` 90
`property_to_expr`	Cohort.DoesNotExist: Cohort matching query does not exist. posthog.tasks.tasks.process_... `Event Count:` 4
`property_to_expr`	NotImplementedError: property_to_expr for element selector only supports exact and is_not operators, not regex ... `Event Count:` 4
`property_to_expr`	NotImplementedError: property_to_expr for element selector only supports exact and is_not operators, not icontains ... `Event Count:` 2
`property_to_expr`	TypeError: Property.init() missing 1 required positional argument: 'key' posthog.ta... `Event Count:` 1