ingest/ncbi: Add `retries` for rules that fetch data

## Description of proposed changes Allow rules that fetch data to retry in case of network errors. Allow 5 retries, which is the usual number we use for the `fetch_ncbi_dataset_package` rule across ingest workflows.¹ Resolves https://github.com/nextstrain/avian-flu/issues/154 ¹ <https://github.com/nextstrain/pathogen-repo-guide/blob/a227dc9485b0291f0d0848168d81a48e15e600ac/ingest/rules/fetch_from_ncbi.smk#L44-L45> ## Checklist <!-- Make sure checks are successful at the bottom of the PR. If applicable, add: - any changes to existing tests - any additional manual testing to confirm changes Please add a note if you need help with adding tests. --> - [ ] Checks pass <!-- 🙌 Thank you for contributing to Nextstrain! ✨ -->