Add `compare_which_columns_differ`

[dave-connors-3]

Description & motivation

This PR adds a new detect_column_changes to help quickly identify which columns have any value-level changes to help narrow down which columns need attention when tracking down differences between two relations.

Checklist

• [x] I have verified that these changes work locally
• [x] I have updated the README.md (if applicable)
• [x] I have added tests & descriptions to my models (and macros if applicable)

[graciegoheen]

Naming ideas:

• compare_which_columns_differ
• columns_with_differences
• identify_columns_with_differences
• compare_columns_mismatch_status
• compare_all_columns_boolean
• compare_shared_columns_status

I'll keep brainstorming.... @dbeatty10 @joellabes lmk if y'all have any ideas!

I'd like the naming to make it clear that:

• this macro checks all columns in 2 tables (or is it only the shared?)
• this macro is only saying true/false are there changes in X columns

On a separate note, I find some of the macro names in this package confusing - would be lovely to spruce up some of the docs so it's clear how each of these are unique (out of scope of this PR):

• compare_column_values
• compare_relation_columns: this is really column schema changes
• compare_all_columns: this is compare_column_values but for all columns?

[joellabes]

I like identify_columns_with_differences, although that might imply it only returns the mismatching columns? Maybe like identify_column_difference_statuses?

[joellabes]

(Swapped my request changes for an approval so you can merge without a second review once you've changed it (or proved that the extra brackets aren't needed))