search: index additional_resources and data_abstract

[GraemeWatt]

Feedback from Sabine Kraml (@sabinekraml):

One significant news is the ample additional material with non-tabular structure that's uploaded on HEPData.
Formerly these were often just SLHA files, but now datasets are increasingly supplemented with code snippets, histfactory models (aka json likelihoods), ML models (ONNX) and more. Some discussion on how this could be standardized, or at least supplemented with appropriate meta data such that these additional resources become searchable and findable in automatic queries, would in my opinion be quite helpful.

We should index the description of the additional_resources to enable free-text searches to return relevant results.

Also, it looks like we only index the publication abstract (from INSPIRE) and not the user-submitted data_abstract (i.e. the comment from the submission.yaml file). The latter might contain additional information specific to the HEPData record and therefore it should also be indexed.