Typed variables in start_session and send_broadcast actions

[rowanseymour]

Moved from nyaruka/goflow#661

[ericnewcomer]

So is the thinking that groups and contacts would accept strings? Not sure how this doesn't also have a goflow component, is there already support for that?

[nicpottier]

For contacts I think it is URN (and maybe UUID?)
For groups maybe it is group name or UUID?

I think those are basically what is currently supported in legacy_vars but we want to type a bit more. (or we just maintain current behavior of trying in priority order)

[ericnewcomer]

Okay, so contacts can already take urns that are expressions? And groups can already accept names that are expressions? And both without uuids?

[rowanseymour]

A group reference can be "concrete", e.g.

{
    "uuid": "",
    "name": "Testers"
}

or "variable", e.g.

{
    "name_match": "@results.group"
}

which is how it works in add|remove group actions. Question is if we can use it that way in these other actions too, and what we'd do for matching contacts by tel and uuid.