Audit & document tracking events for ProblemBank

[kdmccormick]

Context

The old randomized Legacy Library component (LegacyLibraryContentBlock) emits events with the prefix edx.librarycontentblock.content.

The new Problem Bank component (ItemBankBlock) the same events, but with the prefix edx.itembankblock.content.

The eventing docs have not been updated yet: https://docs.openedx.org/en/latest/developers/references/internal_data_formats/tracking_logs/student_event_types.html#content-library-interaction-events

AC

• Confirm that the Problem Bank events correspond to the old Legacy Library block events
  • If not, fix them
• Document edx.itembankblock.content. (could be interleaved with edx.librarycontentblock.content.documentation if that's easier). Mention that the edx.librarycontentblock.content. events are for a deprecated block.
• Add a note to https://docs.openedx.org/en/latest/educators/how-tos/course_development/migrate_legacy_libraries.html that event names will change when converting a legacy Libraries block into a Problem Bank
• Backport to Ulmo