feat: menu search

[nc1z]

Description

This PR implements a simple menu search for the react-router documentation site.

Reason:

• I work at a tech consultancy, and we use react-router quite often across different projects. We often struggle searching through the docs.
• Seems like we're not the only ones who feel this way -> e.g. https://github.com/remix-run/react-router-website/issues/75

Changes Made

• Refactored Menu with a guard clause and for readability
• Extracted the child categories into MenuCategory
• Created Search component
• Updated types

Screenshots or GIFs (if applicable)

Testing

I see that the codebase currently doesn't test its UI components. So I did not add any for now. Do let me know if we want to add some.

Additional Notes

Not a lot of code added, but likely a lot of value for the thousands of react router users 😄

Tagging recent contributors and good sirs for review @brophdawg11 @MichaelDeBoey

[brookslybrand]

Thank you @nc1z for your implementation of simple header search. I'm sorry no one followed up on this, that was definitely my bad.

We're adding search now, thank you for your patience