Jmespath cleanup and followup

[colleenXu]

[RE-ORGANIZING + UPDATING]

There's many jmespath-related issues to follow-up on:

Not done

• MyGene diseaseToGene rev operation: want to retrieve publication info, map to source_url. Should be doable using always_list. Update issues / previous comments when done.
• MyChem chembl.drug_mechanism / MyVariant civic rev operations (issue 1, issue 2): want to retrieve publication info, see older comment for details. Try diff syntax / jmespath_exclude_empty. Update issues / previous comments when done.
• Update BioThings x-bte annotation to use filter #726 (comment): current progress. Once done, make issue for BioThings team to remove outdated params
• writing down exactly how to use filter/jmespath for x-bte annotation. Right now, a lot of info is scattered across Slack, issues, commits, PRs...

Listing info bits for later documentation

• Rohan's doc edits Missing documentation for query options mychem.info#192
• Filter
• Old jumble of jmespath info
• although I didn't end up staying with this format, it has potentially useful links
  • Why I switched format
• always_list param to use with jmespath
• Recent post to Dylan: on what {...} does. Also the syntax for "not existing" field.
• Jmespath_exclude_empty
• Add filter _exists_: for field that is key for operation to all jmespath operations, remove jmespath_exclude_empty from as many operations as possible. Commits here (and one after)
• JMESPath spec (https://jmespath.org/specification.html)

Done

• x-bte operations: replace BioThings list_filter with jmespath #733. Made issue so BioThings team can remove the outdated param.
• review use of jmespath, add always_list parameter when field's value can sometimes be an object (single) and sometimes an array (multiple)
• Review/update x-bte annotation for MyChem drugcentral.bioactivity #780
• MyChem drugcentral bioactivity: write reverse operations #905
• MyChem drugcentral bioactivity: what to do when action_type is missing #904: learned jmespath syntax to use, wrote operations to retrieve this data.
• modify mydisease.info / disgenet to account for score #900: Dylan already made some jmespath examples