Static value in SELECT query (v1.8)

Nobody has claimed this yet.

Hello!
I need add to SELECT query static value to show it in Grafana, but I can't find the way how to do it in InfluxDB. I **don't interested** in adding tag or field. Is it possible?

__Steps to reproduce:__

1. Insert the example values
```sql
INSERT staff,position=worker name="John"
INSERT staff,position=worker name="Michael"
INSERT staff,position=worker name="Frank"
```

__Expected behavior:__
Query with static value and data like in SQLite3, MySQL, etc.

Query:
```sql
SELECT 'IT' AS "data_source", * FROM "staff"
```

Data
```
name: staff
time data_source name position
---- ---- ---- ----
1650305100000000000 IT John worker
1650305100000000000 IT Michael worker
1650305100000000000 IT Frank worker
```

__Actual behavior:__

Error:
```
ERR: field must contain at least one variable
```

__Environment info:__

* System info: Ubuntu 20.04
* InfluxDB version: 1.8 (Docker)

Reproduce the SELECT query against the example staff measurement in an InfluxDB 1.8 environment and confirm the “field must contain at least one variable” error. Review the query behavior for static expressions and define completion as returning the requested data_source column alongside the existing fields without adding a tag or field.

Written by the indexing model from the issue text.