Add multivalue variants to the query language

[jrdh]

This is something I've noticed from using the search interface a bit, particularly during a request from @bwprice recently, was that searching for multiple values on the same field is a pain in the arse but it's also a common use case. Here's an example search: https://data.nhm.ac.uk/search/open-dirty-cheetah which is just trying to find all the specimens matching a set of species names. The or works great but it's a bit arduous to build (particularly if you then want to change the nesting and have to rebuild it but that's another issue...). I can also see this being useful for finding multiple specimens using a set of ids.

Two initial ideas come to mind:

1. Allow the value in string_equals, string_contains and number_equals to take a list of values instead of just a single one.
2. Add new terms for multiple values - string_equals_multi, string_contains_multi and number_equals_multi for example

We also need to decide whether to include any other terms like geo_point or geo_named_area. geo_point to me feels not worth it, whereas geo_named_area may well be.

[jrdh]

Another example use case for this: https://doi.org/10.5519/qd.uqv4g9ys. This request came from Charlotte in the data management team - she had a list of 4131 specimens which a student wanted to capture under one DOI but didn't have a common field that we expose to search on (the EMu field AdmImportIdentifier could have been used but isn't one we expose). Therefore I created 17 number_range terms on the barcodes to find them all because otherwise I would have had to create 4131 string_equal terms in an even bigger or.