[COST-5796] handle Customer.DoesNotExist exception

[djnakabaale]

Jira Ticket

COST-5796

Description

This change adds logging for the IntegrityError to troubleshoot Customer.DoesNotExist exception

Testing

1. Checkout Branch
2. Restart Koku
3. Run unit test and see log message

python3 koku/manage.py test koku.test_middleware.IdentityHeaderMiddlewareTest.test_create_customer_integrity_error_existing_customer

Release Notes

• log IntegrityError to troubleshoot Customer.DoesNotExist exception

* [COST-5796](https://issues.redhat.com/browse/COST-5796) log IntegrityError to troubleshoot Customer.DoesNotExist exception

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.2%. Comparing base (966454e) to head (d272732).
Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #5431   +/-   ##
=====================================
  Coverage   94.2%   94.2%           
=====================================
  Files        370     370           
  Lines      31537   31539    +2     
  Branches    3378    3378           
=====================================
+ Hits       29696   29699    +3     
+ Misses      1197    1196    -1     
  Partials     644     644