Move Director's Notebook category from Newsroom to Blog

[Scotchester]

Addresses https://GHE/CFGOV/platform/issues/3789

Changes

• Move Director's Notebook category from Newsroom to Blog

Testing

1. Pull branch
2. Migrate
3. Create a new blog post, giving it the "Director's notebook" category
4. Ensure it displays properly on the blog listing page and that you can filter by that category

Notes

• Blog post categories are currently not showing up on individual blog post pages. An issue has been opened to potentially address this: https://GHE/CFGOV/platform/issues/3790

Checklist

• PR has an informative and human-readable title
• Changes are limited to a single goal (no scope creep)
• Code can be automatically merged (no conflicts)
• Code follows the standards laid out in the CFPB development guidelines
• Passes all existing automated tests
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future todos are captured in comments
• Visually tested in supported browsers and devices (see checklist below 👇)
• Project documentation has been updated
• Reviewers requested with the Reviewers tool ➡️