Gracefully handle soft-deleted repositories during imports

Problem

In gitlab#350919 (comment 914374563), we noticed that the import of gitlab-org/cluster-integration/auto-build-image/master failed and upon validation, we saw that this repository was soft-deleted as part of #570 (closed).

While we added the ability to gracefully undo a soft-delete at the API level in !884 (merged), we did not do the same at the importer level, so trying to import these repositories leads to a unique constraint violation (path) on the repositories table.

Solution

Update the corresponding query/method used by the importer so that it resets deleted_at and overrides migration_status in case of a path conflict.