[Feature Request] Specify optional expected case for expect_column_values_to_have_consistent_casing

[owenprough-sift]

Is your feature request related to a problem? Please describe.
I have some string columns whose values should always be uppercase and others whose value should always be lowercase. Today, I can use expect_column_values_to_have_consistent_casing to validate that the column is same-cased, but then I would need to add another test to the column to verify that the casing is correct.

Describe the solution you'd like
My .yml files would be more intuitive if there existed an optional expected_case parameter for expect_column_values_to_have_consistent_casing.

Describe alternatives you've considered
Today I use dbt_utils.expression_is_true() to enforce this expectation.