Refactoring sidebars from the app

[shailee-m]

Fixes

Fixes https://github.com/creativecommons/project_creativecommons.org/issues/166 by @brylie

Description

Removing all unused sidebars and only keeping the Page sidebar. Also, added before-footer and after-navigation sidebars.

Checklist

• [x] My pull request has a descriptive title (not a vague title like Update index.md).
• [x] My pull request targets the default branch of the repository (main or master).
• [x] My commit messages follow [best practices][best_practices].
• [x] My code follows the established code style of the repository.
• [ ] I added or updated tests for the changes I made (if applicable).
• [ ] I added or updated documentation (if applicable).
• [x] I tried running the project locally and verified that there are no visible errors.