Add support for getting different versions of objects based on current API version

[zmievsa]

Add support for getting different versions of objects based on current API version

[zmievsa]

This makes a lot more sense than I thought.

For example, if service uses external connectors, we add a separate module for their definitions: "external_connectors.py" and edit them in migrations every time we start using a different version of API of others.

[zmievsa]

I thought about it once again: this is a bad idea. Instead, if-statements with side effects are a much safer choice.

This functionality would render side effect detection useless and will significantly complicate tests of business code so its value is not enough to justify its complexity.

Connectors should be picked with if-statements to make sure that we can measure coverage on them.