Use work_item_types table instead of issue_type column

What does this MR do and why?

First step towards not using the issues.issue_type column so we can drop it in the future in favor of using the work_item_types table #338005 (closed)

We re putting changes that might have an impact on performance behind a feature flag during this effort

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #338005 (closed)