Add CREATE SECRET examples to SQL docs

[kwannoel]

Context

Slack request on 2026-02-17:

• "Please create a documentation issue for missing CREATE SECRET docs examples. Include marker docs-eval-1771366574996."

Marker: docs-eval-1771366574996

Related docs context search surfaced recent SQL documentation refinements and example-oriented updates:

• docs: clarify temporal join distribution key requirements #924
• docs: Document streaming_use_snapshot_backfill for isolation in streaming job creation #880

Problem

The docs currently do not provide clear, concrete examples for CREATE SECRET usage. This makes it hard for users to quickly understand valid syntax and how secrets should be referenced in downstream SQL objects (for example, connectors and other resources that require credentials).

Suggested Fix

1. Add a dedicated CREATE SECRET examples section in the relevant SQL docs page (or create a focused page if it does not exist).
2. Include copy-paste-ready examples covering:
   • Minimal CREATE SECRET statement.
   • Example with quoted/special-character secret values.
   • Referencing secrets from practical workflows (for example CREATE CONNECTION, CREATE SOURCE, and CREATE SINK where applicable).
3. Add lifecycle examples for updating/rotating and deleting secrets (with links to the corresponding SQL statements if those operations are documented separately).
4. Cross-link the examples from related SQL pages so users can discover secret usage where they configure external systems.
5. Validate example syntax against current behavior and add short notes on security best practices (for example avoiding plain credentials directly in DDL).