feat(ibm-no-nullable-properties): add new spectral-style rule

[padamstx]

PR summary

This commit introduces the new spectral-style rule 'ibm-no-nullable-properties', which will warn about the presence of nullable schema properties in schemas other than JSON merge/patch requestBody schemas (where nullable properties are allowed).

PR Checklist

General checklist

Please make sure that your PR fulfills the following requirements:

• [x] The commit message follows the Angular Commit Message Guidelines.
• [x] Tests for the changes have been added (for bug fixes / features)
• [x] 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:

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

[padamstx]

I think I've addressed all the review comments

[ibm-devx-sdk]

:tada: This PR is included in version 1.3.0 :tada:

The release is available on npm package (@latest dist-tag)

Your semantic-release bot :package::rocket:

[ibm-devx-sdk]

:tada: This PR is included in version 1.8.0 :tada:

The release is available on npm package (@latest dist-tag)

Your semantic-release bot :package::rocket:

[ibm-devx-sdk]

:tada: This PR is included in version 1.8.0 :tada:

The release is available on npm package (@latest dist-tag)

Your semantic-release bot :package::rocket: