Variables couldn't be exported to Dashboard

Hello, InfluxDB community.
I need help with getting variables by query and their use in the dashboard.

## Environment
InfluxDb v2.1.1

## Metrics
I have metrics with name: `http_client_requests`
Tags: "method", "status", "uri", "myCustomTag"

## Variable `myCustomVar`

```
from(bucket: "mymetrics")
|> range(start: v.timeRangeStart, stop: v.timeRangeStop)
|> filter(fn: (r) => r["_measurement"] == "http_client_requests")
|> keyValues(keyColumns: ["id"])
|> group()
|> keep(columns: ["id"])
|> distinct(column: "id")
|> keep(columns: ["_value"])
|> yield()
```

### Result
I see the result of the variable query. But I can't get the same result in the metrics dashboard.


> I'd like to see `_value` in the metrics dashboard.

## Metrics Dashboard
There I'm using the var `myCustomVar`.

```
from(bucket: "mymetrics")
|> range(start: v.timeRangeStart, stop: v.timeRangeStop)
|> filter(fn: (r) => r["_measurement"] == "http_client_requests")
|> filter(fn: (r) => r["_field"] == "count")
|> filter(fn: (r) => r["status"] == "200")
|> filter(fn: (r) => r["id"] == v.myCustomVar)
|> count()
```

Then I open the dashboard in the same time range but it couldn't get the var values.

Reproduce the issue using the `myCustomVar` variable query and the metrics dashboard query shown in the report on InfluxDB v2.1.1. Start by comparing the variable query result with how the dashboard substitutes `v.myCustomVar`; done means the dashboard receives the variable values and applies the `id` filter as expected.

Written by the indexing model from the issue text.