Imports / Exports in Rails Cheatsheet is outdated per updates made in 12.1
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### Problem to solve
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### Proposal
Currently, our cheatsheet reflects this code snippet to check for Import/Export errors:
```
# Find the project and get the error
p = Project.find_by_full_path('<username-or-group>/<project-name>')
p.import_error
# To finish the import on GitLab running version before 11.6
p.import_finish
# To finish the import on GitLab running version 11.6 or after
p.import_state.mark_as_failed("Failed manually through console.")
```
As of 12.1, the column that allowed us to call the attribute `:import_error` was removed per [this Merge Request](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/14288).
We should remove this section and replace with a redirect to the Project import status API.
### Who can address the issue
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### Other links/references
Discovered when working on [this ticket](https://gitlab.zendesk.com/agent/tickets/173892) (ZD Internal)
issue