Allow combining hashes and nested hash arrays

What does this MR do?

!67922 (merged) introduced rules flattening, this MR allows combining hashes and nested arrays of hashes for increase flexibility. This was the original idea of #322992 (closed).

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
  • This fixes a regression for an unreleased feature.
• I have added/updated documentation, or it's not needed. (Is documentation required?)
  • Docs are in !68283 (comment 652679126)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.