Code sample for sql.to()/from() should use secrets API

In this section: https://awesome.influxdata.com/docs/part-2/querying-and-data-transformations/#accessing-external-data-sources

The code for ```from()```:
```
sql.from(
  driverName: "postgres",
  dataSourceName: "postgresql://user:password@localhost",
  query:"SELECT * FROM TestTable"
)
```
I suggest that we demonstrate using ```import "influxdata/influxdb/secrets"``` throughout.

