feat(bulk-import): perform more dry-run checks in the POST /imports…

… backend endpoint [RHIDP-3339] (#1979)

* Add test highlighting the expectations

* Improve import dry-run checks

Besides checking if the specified 'catalogEntityName' already exists in
the catalog:

- Check if the repo is empty
- Check if the repo already has a catalog-info YAML file in its default
  branch

* Fix code duplication issues reported by static code analysis

* Check the CODEOWNERS file presence in the repo as a new dry-run operation

On the register existing entity form,
there is this "Use codeowners file" checkbox
which reads from the CODEOWNERS file in the repo.
The import might fail if entity owner name is missing or
if no codeowners file is present in the repo.

Co-authored-by: Debsmita Santra <dsantra@redhat.com>

* Fix issues reported by SonarCloud

- Refactor to reduce code duplication in githubApiService.ts
- Explicitly set a compare function when sorting the dry-run import statuses array
- Reduce level of nested functions in router.test.ts

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Co-authored-by: Debsmita Santra <dsantra@redhat.com>