Extract LfsPointersFinder from ExtractPath

Contributes to https://gitlab.com/gitlab-org/gitlab/-/issues/330406

**Problem**

Method `lfs_blob_ids` is tightly-coupled with ExtractPath module. It
makes it diffucult to reuse it.

**Solution**

1. Create LfsPointersFinder to fetch blob ids by repository and path.
2. Replace old code with LfsPointersFinder implementation