Push HeartRate and Step Counts to Nightscout API v3

This is a Feature request -- I have already implemented this in a fork and will follow up with a PR for review in the coming days.

Issue:
Currently, activity data is collected by the Wear app but is not used very heavily within AAPS (essentially just automations). The data remains locked within AAPS.

I have a need to use this data for further analysis and so want to sync it to Nightscout with the rest of my data.

Nightscout API v1 currently supports an activity collection.
Nightscout API V3 does not, but APIv3 does support a polymorphic entries collection that can technically and logically hold activity data with no modifications.

Option 1:
Use entries collection to push documents of type activity with heartrate records at a max granularity of 1 reading per minute delivered in 5 minute batches and step count records with a max granularity of 1 record per 5 minutes.

Option 2:
Simultaneously update Nightscout to extend APIv3 to support the existing activity collection. Push Heatrate and stepcount data to that collection.

I have chosen option 1 -- Minimal changes to AAPS are required and no changes needed to nightscout.

Start by reviewing the Wear app's collected activity data and the Nightscout API v3 polymorphic entries collection described in the issue. The selected approach is complete when heart-rate and step-count records are pushed as entries at the stated granularities and batch interval, with the existing fork or follow-up PR providing the implementation details.