fixing headings in edu lesson jump menus, adding generateHash

[stephiescastle]

Checklist

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Description

Follow up to:

• https://github.com/nasa-jpl/www/issues/99#issuecomment-2318156030

• Ensures that a heading will not appear in the Jump Menu navigation if the heading's section doesn't contain content.

• Also adds an unrelated generateHash utility function. www will use this.

Instructions to test

1. make vue-storybook
2. View the EDU Lesson story
3. Note that the overview section is missing both from the page and the jump menu

Tested in the following environments/browsers:

Operating System

• macOS
• iOS
• iPadOS
• Windows

Browser

• Chrome
• Firefox ESR
• Firefox
• Safari
• Edge