docs: improve DefaultApi.md examples and add common-patterns preamble

[onesignal-deploy]

Documentation updates

Improvements to the generated DefaultApi.md example snippets:

• New common-patterns preamble at the top of DefaultApi.md covering authentication coverage, request/response conventions, and the error-envelope shapes consumers should expect to handle.
• Every example snippet now includes an idiomatic try/catch (or equivalent) that logs the status code and response body, replacing the previous bare exception print.
• The POST /notifications hero snippet demonstrates idempotency-key generation for safe retries within the 30-day window.
• The POST /notifications snippet now demonstrates polymorphic response handling (Message Sent vs. Message Not Sent) instead of an unsafe single-shape access.
• Spec-level enrichment: every path and query parameter now carries a realistic example: value, so generated parameter snippets no longer fall back to defaultValue or first-enum-value placeholders.

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Generated from OneSignal/api-client-libraries@3b35d43...6d24a5c.