Android - tweaks to heartbeat collection subscription (part 1)

[bplattenburg]

Today, we automatically subscribe any device using the hearbeat tool to the entire dittotools_devices collection, but that doesn't scale to production across multiple locations.

We either need to provide a way to disable this subscription (which has the downside of breaking multihop for a device which can't see the big peer e.g. lost LAN but still has BLE) or provide the ability to scope it to a more limited query like "devices at the same locationId as this device"

Note - we should also pair any limited query here with a matching eviction query to cover devices changing location and other edge cases

[bplattenburg]

In the short term, the path forward here is to use publishToDittoCollection in the heartbeat config to control whether to subscribe to the collection.

Longer term, I'll break out a story (link to be added here) to narrow the subscription to something like "devices in the same location" to allow for flooding & multihop to get data out without pulling data in from remote devices

[bplattenburg]

Part 2 (location-specific subscriptions) broken out into #84