Replace db.statement with db.query.text in examples

[lmolkova]

Follow up for #866

db.statement was renamed to db.query.text, this PR updates examples and other mentions

Merge requirement checklist

• CONTRIBUTING.md guidelines followed.
• Change log entry added, according to the guidelines in When to add a changelog entry.
  • If your PR does not need a change log, start the PR title with [chore]
• schema-next.yaml updated with changes to existing conventions.