`tbl_hierarchical()` enhancements

[edelarua]

Enhance tbl_hierarchical() with the following features:

• @edelarua to investigate other nested data table structures and we will discuss which to support.
  https://github.com/insightsengineering/sme-tasks/issues/754
• Investigate how we could/should use over_variables when it's not just a single row, e.g. over AESEV or Grade.
  • Maybe it's easier to just include an example of creating two tables separately and stack to illustrate how to create these tables.
• Add functionality to accept unnamed integers in the digits argument like other functions. (maybe we should just re-add (assign_summary_digits()) @ddsjoberg #2080
• Should cards::ard_hierarchical() and the count function optionally include the attributes from the data frame so we can use them in the header? I wonder if it's necessary? The ARD-first approach for these tables are not really general, so the utility of this function is pretty limited. If I needed an ARD, it may be best to just create the table, then grab the ARD from the table object..... 🤔
• Add a function to sort and filter AE summary tables? (S3 methods) @edelarua
  Add S3 methods to sort and filter hierarchical tables #2096

tbl_ard_hierarchical() Updates

• Update tbl_ard_hierarchical() with structural checks of the ARD inputs
• Update tbl_ard_hierarchical() with overall_row argument