Add import work items policy

What does this MR do and why?

Slight modification to import work items policy.

• Use import_work_items instead of create_work_item since bulk imports of work items should have a separate permissions category.
• Remove unneeded Requirements license check since it's already part of the policy check.

This feature is still behind a feature flag. See #379153 (closed) for list of MRs.

Screenshots or screen recordings

No user-facing changes.

How to set up and validate locally

!112271 (merged) has instructions for setup.

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 #379153 (closed)