Bug 1933716

Description of problem:
Having a Satellite with container type repositories synced and migrated to pulp3, consequential attempts to sync the repos to the external capsule fail.


Version-Release number of selected component (if applicable):
6.9.0 snap 12
python3-pulp-container-2.1.0-1.el7pc.noarch
tfm-rubygem-pulp_container_client-2.1.0-1.el7sat.noarch


How reproducible:
always


Steps to Reproduce:
1. Have a Satellite with registered external Capsule (Library LCE)
2. Sync some container images to the Satellite using Products > Repo Discovery
   (I used quay/busybox and registry.redhat.io/dotnet/dotnetcore-10-rhel7)
3. Run content migration and switchover (succeeds)
4. Trigger the Capsule sync


Actual results:
Capsule sync fails with error
Katello::Errors::PulpError: PLP0000: 500 Server Error: 'Internal Server Error' for url: https://<SAT>/v2/default_organizationnet_core-dotnet_dotnetcore-10-rhel7/manifests/1.0


Expected results:
Successful sync


Additional info:
Traceback:
[2021-02-22 16:50:44 +0000] [1909] [ERROR] Error handling request
Traceback (most recent call last):
File "/usr/lib64/python3.6/site-packages/aiohttp/web_protocol.py", line 418, in start
resp = await task
File "/usr/lib64/python3.6/site-packages/aiohttp/web_app.py", line 458, in _handle
resp = await handler(request)
File "/usr/lib/python3.6/site-packages/pulp_container/app/registry.py", line 144, in get_tag
return await Registry.dispatch_converted_schema(tag, accepted_media_types, path)
File "/usr/lib/python3.6/site-packages/pulp_container/app/registry.py", line 191, in dispatch_converted_schema
schema, converted, digest = schema1_converter.convert()
File "/usr/lib/python3.6/site-packages/pulp_container/app/schema_convert.py", line 42, in convert
converted_schema = self._convert_schema(legacy)
File "/usr/lib/python3.6/site-packages/pulp_container/app/schema_convert.py", line 57, in _convert_schema
return converter.convert()
File "/usr/lib/python3.6/site-packages/pulp_container/app/schema_convert.py", line 101, in convert
self.compute_layers()
File "/usr/lib/python3.6/site-packages/pulp_container/app/schema_convert.py", line 133, in compute_layers
layer_id, fs_layer, last_layer=(i == fs_layers_count - 1)
File "/usr/lib/python3.6/site-packages/pulp_container/app/schema_convert.py", line 177, in _compute_v1_compatibility_config
container_config=dict(Cmd=fs_layer.history["created_by"]),
KeyError: 'created_by'