docs: add missing CREATE SECRET examples in SQL docs

[kwannoel]

Context

Slack transcript (no thread URL provided):

• [2026-02-17T21:51:29.118Z] <@U0AG7B6P9AL>: <@U0AF0DZ7C9Y> /docs Please create a documentation issue for missing CREATE SECRET docs examples. Include marker docs-eval-1771365088973.

Marker: docs-eval-1771365088973

Related context from docs pipeline search:

• The returned docs matches are mostly unrelated pages (for example cloud onboarding/operations pages) and did not surface a clear CREATE SECRET example location.
• Recent docs PR matches are generic and do not indicate dedicated CREATE SECRET example coverage.

Problem

Users are asking for CREATE SECRET documentation examples, which indicates the current docs are missing practical examples or the examples are hard to discover. Without examples, users may be unsure how to define secrets and reference them in SQL workflows.

Suggested Fix

1. Add a dedicated examples section for CREATE SECRET in the relevant SQL reference page.
2. Include at least two end-to-end examples:
   • A minimal CREATE SECRET statement.
   • A usage example that references the created secret from another SQL object/config (for example a connector/source/sink configuration that uses a secret reference).
3. Add brief notes on common pitfalls (naming, permissions, and how to verify the secret is referenced correctly).
4. Add cross-links from related SQL pages where users are likely to need secrets so the examples are easier to find.