Conflicting Domain creation at the same time results in an ISE (500)

[jlsherrill]

Version
3.29.1

Describe the bug
if multiple requests are dispatched to pulp at the same time to create a domain with the same name, pulp will return an ISE instead of a proper 400 (bad request).

To Reproduce
trigger multiple requests:

http --auth admin:password  localhost:8080/pulp/default/api/v3/domains/  name=foo2  storage_class="pulpcore.app.models.storage.FileSystem"  storage_settings[location]="/var/lib/pulp/foo2"  &
http --auth admin:password  localhost:8080/pulp/default/api/v3/domains/  name=foo2  storage_class="pulpcore.app.models.storage.FileSystem"  storage_settings[location]="/var/lib/pulp/foo2" &

One will result in an ISE, while the other creates the domain. If i try again after its created, i get a proper 400 Bad Request.

Expected behavior

I'd expect a 400 or 409

Additional context
We can't pre-create the domains, nor can we control when the requests come in that need a domain created, so we can't avoid this situation. We've worked around it for now, so i wouldn't consider this a high priority, but it does prevent us from detecting actual 500s if they were to occur as easily. (Right now we just assume its a conflict).