Provide examples using `time` and aggregate functions in Grafana

> You can group by columns other than time.

@sanderson True, but Grafana specifically requires a `time` column in the result and Flight SQL (or IOx?) doesn't know how to resolve `iox.[measurement].time` unless you group or partition by time. At least, as far as I can tell.

```sql
-- This works in Grafana:
-- SELECT avg(temp) OVER(PARTITION BY DATE_BIN(INTERVAL '2 hours', time, '1970-01-01T00:00:00Z'::TIMESTAMP)) AS AvgTemp,
-- DATE_BIN(INTERVAL '2 hours', time, '1970-01-01T00:00:00Z'::TIMESTAMP) AS time
-- FROM iox.home

-- So does this:
-- SELECT avg(temp) AS AvgTemp, DATE_BIN(INTERVAL '2 hours', time, '1970-01-01T00:00:00Z'::TIMESTAMP) as time
-- FROM iox.home
-- GROUP BY DATE_BIN(INTERVAL '2 hours', time, '1970-01-01T00:00:00Z'::TIMESTAMP)

-- Grafana doesn't like this; it wants a time column. It works in Superset and other clients.
-- SELECT avg(temp)
-- FROM iox.home

-- IOx (SQL) doesn't like this, as in "what time value am I supposed to return?".
-- SELECT DATE_BIN(INTERVAL '2 hours', time, '1970-01-01T00:00:00Z'::TIMESTAMP) as time, avg(temp) AS AvgTemp
-- FROM iox.home
```

No documentation file or test is named in the issue. Start by reviewing the existing SQL and Grafana documentation for query examples, then add examples covering time columns and aggregate functions; done means the examples explain the expected query shape for Grafana and other clients.

Written by the indexing model from the issue text.