Telemetry client for remote channel environment

[vkottler]

Need a "message type" prefixed messaging protocol.

Use the existing length-prefixed messaging protocol.

When initializing expect configuration data / messages to learn full set of channels, after initialization channels come using vtelem-style messages:

• header: number of channels
• channel ID array: integer channel identifiers
• channel value array: raw channel values

[vkottler]

For exposing/listening: configure a mapping of environment name + protocol/factory, start listeners when bringing application up (handled by runtimepy)

edit: a telemetry serving thing only needs to be given an environment name

[vkottler]

JSON server could be responsible for all "channel environment metadata" transfers, that we we only need the telemetry serialization / messaging.

the "channel IDs" "channel values" tech could just be a new connection type

[vkottler]

Should be able to:

• query any channel environment by name from JSON conn
• query current app config from JSON conn?

it would nice to be able to query the server for telemetry ports?

maybe the telemetry connection should be multi-channel-environment?

[vkottler]

Event stream (both to and from): #176

We should implement writing to and reading from a file. Realistically it will be more like writing an entire directory for each channel environment, for the JSON metadata.

Probably something like:

<env name 1>/
    file1.json
    file2.json
    ...
<env name 1>.bin
...

[vkottler]

Yeah may as well implement highest-possible fidelity "sample all events for all environments" option first, see how useful that is.

[vkottler]

we have the UI now + UDP struct messaging etc.