Add restrict_with_error to docs

What does this MR do and why?

This MR adds a note to our developer documentation to recommend using dependent: :restrict_with_error to make sure child objects are cleaned up before calling .destroy on the parent object.

This topic was already described in 3 different places in docs all for different reasons. As such I've added cross-linking between all of them to make this easier to find if someone lands on one of the other sections.

MR acceptance checklist

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