Regexp_intr shim support for dbt-expectations macro

Since dbt-expectations removed support for the Databricks and Spark macro compatibility of their macros, I believe it would be best to move some support of these macros into this package.

I currently have a working version of the `regexp_instr` macro for spark that is outlined within the dbt-expectations [PR #226](https://github.com/calogica/dbt-expectations/pull/226). Claus makes a great point to instead move this PR into this project. Before moving forward with opening a PR I wanted to confirm this approach is the desired way forward within this Issue. Specifically, I noticed the last release was almost a year ago. Would you prefer to continue adding to this project, or is this a shim we should instead provide for our packages within fivetran_utils?

Let me know what you feel the best path forward would be. Thanks!