[Feature Request] Allow regex flags/parameters in regexp_instr and calling tests

[tconbeer]

Is your feature request related to a problem? Please describe.
I would like the regex I provide to expect_column_values_to_match_regex_list and similar tests to be case-insensitive, but currently that is not possible.

Postgres, Snowflake, and Redshift support an argument (called flags in pg and parameters in the others) for this. BigQuery does not, but the column could be lowercased before being passed into regexp_instr.

Describe the solution you'd like
Add a flags argument to expect_column_values_to_match_regex_list and other regex-based tests that accepts a string value and passes it through to the underlying database implementation.

Describe alternatives you've considered
Rolling my own test.

Additional context
I'm happy to contribute this if there is interest.

[clausherther]

@tconbeer Thanks for this feature request! This seems like a useful and worthwhile addition, happy to take any PRs.