sql: include placeholder values in SHOW QUERIES

[jseldess]

Jesse Seldess (jseldess) commented:

PR: cockroachdb/cockroach#66689

From release notes:

The [SHOW QUERIES](../v21.2/show-statements.html] command was extended for prepared statements to show the actual values in use at query time, rather than the previous $1, $2, etc. placeholders. We expect showing these values will greatly improve the experience of debugging slow queries. [#66689][#66689) {% comment %}doc{% endcomment %}

Jira Issue: DOC-1393