CALL ... YIELD Documentation not added yet

The syntax structure and usage documentation of CALL ... YIELD has yet to be added.

A basic example:

```postgresql
SELECT *
FROM cypher('test', $$
MATCH (v)
CALL label(v) YIELD label AS l_v
RETURN l_v
$$) as (labels agtype);
```

No file is named in the issue; first locate the AGE website documentation section covering CALL and YIELD and review nearby syntax pages. Use the supplied PostgreSQL example to document the syntax and usage, with completion marked by a published section covering both.

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