Revert to using multitenancy_enabled in application.yml

[citizenrich]

Hi folks. So, it seems a relatively recent PR changed the config to toggle multitenancy off/on. The way it is toggled on is to uncomment like so:

    partitioning:
#      allow_references_across_partitions: false
#      partitioning_include_in_search_hashes: false

See: #200

The issue, besides the above being unintutive, is that this doesn't work for environment variables (like the configs I've tried which do support env vars). I wonder if there is interest in reverting to the previous approach, which explicitly calls out the config, with multitenancy_enabled: true. IMHO this would be intuitive and can be changed in the environment. Thoughts?

[citizenrich]

@jtheory

[citizenrich]

So, for those looking for the setting, at least in v5.4.1, hapi.fhir.partitioning.enabled is seen by the config parser, even if it is not in application.yml.