fix(ibm-required-array-properties-in-response): avoid errors in allOf elements w/o required keyword

[padamstx]

PR summary

Fixes #690
This PR fixes the issue by bypassing our error checks for
any allOf element schema that does not include a 'required' field.

PR Checklist

General checklist

Please make sure that your PR fulfills the following requirements:

• The commit message follows the Angular Commit Message Guidelines.
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• Dependencies have been updated as needed
• .secrets.baseline updated as needed?

Checklist for adding a new validation rule:

• Added new validation rule definition (packages/ruleset/src/rules/*.js, index.js)
• If necessary, added new validation rule implementation (packages/ruleset/src/functions/*.js, updated index.js)
• Added new rule to default configuration (packages/ruleset/src/ibm-oas.js)
• Added tests for new rule (packages/ruleset/test/*.test.js)
• Added docs for new rule (docs/ibm-cloud-rules.md)