wrap user observer creation in unique_constraint_retry
wrap user observer creation in unique_constraint_retry

closes #CNVS-22628

Change-Id: Ie1a997653d70fe5062295ff5b5e5fb7c2b32fe4c
Reviewed-on: https://gerrit.instructure.com/61738
Tested-by: Jenkins
Reviewed-by: Jon Willesen <eb5ce5e6a76c243326fecfa94534101600f87bd9@instructure.com>
Product-Review: James Williams  <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>
QA-Review: James Williams  <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>

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