Add DOIs for Ingest retroeval

Merged PR: https://github.com/acl-org/acl-anthology/pull/8682

## DOI tasks

- [ ] Generate the DOIs for all volumes (`generate_crossref_doi_metadata.py`)
- [ ] Upload to [Crossref](https://doi.crossref.org/servlet/home)
- [ ] Add the DOIs to the XML (`add_dois.py`)

Start by reading `generate_crossref_doi_metadata.py` to confirm how volume DOI metadata is generated. Run it for the Ingest retroeval set, then use its output with `add_dois.py` to apply DOI fields into the target XML files. Verify the updated XML includes DOIs for all intended volumes, and then follow the issue’s Crossref upload step via the linked portal URL. Done means retroeval volume XML is updated with DOIs and the Crossref submission is completed.

由索引模型根据 Issue 内容生成。