Scc 3874

[danamansana]

Adds support for a new subject_prefix search parameter for SCC-3874
The approach taken parallels the existing implementation of the subject param.
Specific Changes:

• Adds subject_prefix in ADVANCED_SEARCH_PARAMS and SEARCH_SCOPES for param extraction
• Adds subject_prefix as a new case in building the ElasticQueryBuilder query
• Currently adds some boosting for exact matches on subjectLiteral.raw in this case. The current boost is 50, could change that value
• Adds a new test for this case
  Also:
• a small unrelated addition to .gitignore for local files

[nonword]

Still need these debugs?

[danamansana]

I'd leave them in myself, but can remove them if that seems better

[danamansana]

Made some changes following PR suggestions.
The query being generated is a bit different now. Previously it was more highly nested, so bool->must->bool->must->bool->should instead of bool->must->bool->should , and that bool->should->term which is supposed to be boosting exact matches on subjectLiteral.raw was also nested under the bool->should clause. The current query seems correct to me, but let me know if it seems wrong.
Also, I have added boosting for exact matches on parallelSubjectLiteral.raw, let me know if that isn't desired.