Reduce complexity of Chain::Config::Content

This issue is a follow up from this MR review: !20179 (comment 254548965)

We need to wait until !20179 (merged) and !21041 (closed) are both merged before we can refactor Chain::Config::Content.

An idea of refactoring is in !20179 (comment 254548965)

I agree this class is currently complex but it's also due to the feature flag as we have duplicate logic. That would go away in the next release. I agree with the intention in your proposal but I'd like to wait until we merge this and parent/child pipelines before refactoring this. The reason is that in parent/child pipelines we have a special case added to this class that may not fit this refactoring.

Once it's all in place it would be easier to see what refactoring fits the class. I'll create an issue now to follow up after parent/child pipelines.