AQG-443: document DDSQL's akeys and avals functions (#32714)

* AQG-443: document DDSQL's `akeys` and `avals` functions

These newly added functions operate on the `hstore` type. Since the only place in the docs where `hstore` is mentioned is the section about `Tags`, this PR adds a new subsection there that documents `hstore` functions, loosely following [Postgres' docs](https://www.postgresql.org/docs/8.4/hstore.html) for description.

* AQG-443: use singular for tag when used in a genitive sentence

Co-authored-by: Zakaria Fikrat <113985839+zafikrat@users.noreply.github.com>

* AQG-443: use correct casing, verb time and order of function params

Co-authored-by: May Lee <may.lee@datadoghq.com>

---------

Co-authored-by: Zakaria Fikrat <113985839+zafikrat@users.noreply.github.com>
Co-authored-by: May Lee <may.lee@datadoghq.com>

Author: 3 people

content/en/ddsql_reference/_index.md

@@ -808,9 +808,6 @@ ORDER BY value DESC;{{< /code-block >}}
 </table>
 
 
-
-
-
 ## Tags
 
 DDSQL exposes tags as an `hstore` type, which is inspired by PostgreSQL. You can access the values for specific tag keys using the PostgreSQL arrow operator. For example:
@@ -840,6 +837,21 @@ FROM k8s.daemonsets da INNER JOIN k8s.deployments de
 ON da.tags = de.tags -- for a specific tag: da.tags->'app' = de.tags->'app'
 ```
 
+Additionally, you can extract tag keys and values into individual arrays of text:
+
+```sql
+SELECT akeys(tags), avals(tags)
+FROM aws.ec2_instance
+```
+
+### HSTORE functions and operators
+
+| Name                                          | Return type   | Description                                                                                      |
+|-----------------------------------------------|---------------|---------------------------------------------------------------------------------------------------
+| tags -> 'text'                                  | Text          | Gets the value for a given key. Returns `null` if key is not present.                             |
+| akeys(hstore tags)                            | Array of text | Gets the keys of an HSTORE as an array                                                            |
+| avals(hstore tags)                            | Array of text | Gets the values of an HSTORE as an array                                                          |
+
 ## Further reading
 
 {{< partial name="whats-next/whats-next.html" >}}