Feature: persist feed configuration to disk

[lthurston]

Description

Not being able to persist and deploy feed configuration is a pain point with Feed Me, and a non-starter for organizations that reasonably demand that all project configuration is able to be deployed in an automated manner. This draft PR is a step in that direction. There are more details on the PR.

#1399

[bas-net]

Any update on this? We are running into the same issue. We'd like our feeds to be deployable as well so we can test it in an acceptance env and then run it on prod data.