template task groupBy not accepting duration as number or string

It looks like the template feature won't allow you to group by time as well as a few other tags.

The important bits:

Template:

var groupBy = [*]

var data = batch
|query(query)
.groupBy(groupBy)
.period(period)
.every(every)
.align()
.alignGroup()

Json:

"groupBy": {
"type": "list",
"value": [
{
"type": "duration",
"value": "10s",
"description": ""
},
{
"type": "string",
"value": "host_name",
"description": ""
},
{
"type": "string",
"value": "host_ip",
"description": ""
}
],
"description": ""
}

This generates `invalid var groupBy: unexpected var type duration, value is a string`

"groupBy": {
"type": "list",
"value": [
{
"type": "duration",
"value": 10000000000,
"description": ""
},
{
"type": "string",
"value": "host_name",
"description": ""
},
{
"type": "string",
"value": "host_ip",
"description": ""
}
],
"description": ""
}

Generates `invalid var groupBy: unsupported Var type json.Number`

Start at the template task groupBy parsing and variable conversion entry point, then reproduce the two JSON examples from the issue. Trace how duration strings and numeric values are handled in a list, and verify that valid duration values no longer produce either reported error.

Written by the indexing model from the issue text.