keep gender_mf metadata in yaml files synced with database

[carmichaelong]

When "download data" on the app is used, it currently pulls the pre-existing sessionMetaData.yaml from the session. However, this file seems to always have the key gender_mf with associated with the value m when downloading from the app.

Some possibly useful parts of the code to trace the calls:

• Section from Viewer's Download Data button: https://github.com/stanfordnmbl/opencap-viewer/blob/7175921efae8d00901e44cb75c2bddc137a97a40/src/components/pages/Session.vue#L309
• Calls code to downloadSessionArchive
• Calls to API: async_download -> download_session_archive -> SessionDirectoryConstructor -> build -> collect_docs

To-dos:

• Find and fix where in core where static/neutral trial creates the .yaml file and posts to AWS (this might have been fixed by [Under review] - Fix problem with gender_mf field in downloaded files. opencap-core#208)
• Figure out a strategy for dealing with older yaml files. Determine if it would be costly to update the .yaml file on AWS each down Download Data is used
• (already done) Fix yaml file when downloaded using core API ([Under review] - Fix problem with gender_mf field in downloaded files. opencap-core#208)