This aims towards bringing in multi-tenant channel bundle endpoints,
for example suitable to accepting TTS/TTN payloads, in order to run
a network of multiple devices on a single TTN application conveniently.

The feature is called "device addressing" (DA).

Examples:

- mqttkit-1/d/123e4567-e89b-12d3-a456-426614174000
- mqttkit-1/dt/network-gateway-node

It works with both MQTT and HTTP protocols.

Add more details about per-device decoding to the `WanBusStrategy`, and
exercise a few topic/channel decodings, including edge cases.

Examples:

- myrealm/acme/area-42/foo-70b3d57ed005dac6
- myrealm/d/123e4567-e89b-12d3-a456-426614174000
- myrealm/dt/acme-area42-eui70b3d57ed005dac6
- myrealm/dt/eui-70b3d57ed005dac6
- myrealm/dt/acme-area42-eui70b3d57ed005dac6
- myrealm/dt/acme-area42-eui70b3d57ed005dac6-suffix
- myrealm/dt/myrealm-acme-area42-eui70b3d57ed005dac6
- mqttkit-1/d
- myrealm/dt

For the new SensorWAN "direct" addressing scheme, by getting rid of the
previous `/d` vs. `/dt` path fragments, and using `/device` vs.
`/channel` instead, it reduces confusion about the meaning of those
prefixes, and makes usage less error prone.

By defining a `direct_channel_allowed_networks` setting on the
application configuration, the direct access to the corresponding
channel will be restricted to the specified networks/owners.