Add `out_column` attribute to all transforms

[alex-hse-repository]

🚀 Feature Request

Make transforms save out columns in out_column attribute.

Motivation

More convenient approach to handle out columns

Proposal

• For every transform create attribute self.out_column: List[str] and save the list of transform's out columns in this attribute.
• Make sure that transforms save out columns in all cases(even in inlace mode)

Test cases

Test that transforms saves out columns in attribute self.out_column in all cases

Alternatives

No response

Additional context

No response

Checklist

• [ ] I discussed this issue with ETNA Team