Update DSS Similarity Factory

[maxkadel]

What maintenance needs to be done?

The LegacyBM25SimilarityFactory is deprecated for Solr version 9, so this will have to be updated prior to upgrading. This can change relevancy rankings, so we will want to confirm that the new relevancy rankings are acceptable, or align them with the current rankings (see PR for Catalog similarity factory replacement for an example)

Level of urgency

• High
• Moderate
• Low

Why is this maintenance needed?

• We want to move to Solr 9 before Solr 8 is no longer getting security patches

Acceptance criteria

• DSS uses BM25SimilarityFactory (non-legacy version)
• The resulting relevancy is acceptable to stakeholders