Remove prevent rule for read_work_item_type in type_policy

Issue: [BE] Ensure privileges, policies and abilities ... (#581944)

What does this MR do and why?

Fixes the custom type policy to allow reading custom work item types even when the configurable_work_item_types license is not available.

Previously, prevent :read_work_item_type was applied when the license was unavailable, which caused a GraphQL error when listing work items with custom types after a downgrade, the workItemType field is null: false but returned nil because the type couldn't be read.

This replaces the :read_work_item_type prevention with :admin_work_item_lifecycle, so that:

• Custom types remain readable after a license downgrade (existing items continue to work)
• Lifecycle administration is still gated on the license
• Cross-namespace access is unchanged (handled by the policy's delegate to namespace | organization)
• create_work_item_type / update_work_item_type are already prevented in the group and organization policies, so no duplication is needed here

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• Discussion thread

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