Fix ugly looking navigation on mobile

[Blargian]

Summary

I'm sure there are very few people looking at ClickHouse docs on mobile... never the less, the secondary (docs) navigation bar looks horrible on mobile:

This PR adds custom React components Hamburger, HamburgerMenu and MobileMenu (grouped under DocsCategoryMobileNav) such that the secondary menu acts in a similar way to the primary menu (displays a burger menu and navigation overlay for smaller screen sizes).

Result

Still to do:

• Fix search bar styling for dark theme.
• Hide navbar when link is clicked.
• Move dropdownCategories in src/theme/NavBar/Content/index.js to it's own config file, accessible by this new component.

Checklist

• Delete items not relevant to your PR
• URL changes should add a redirect to the old URL via https://github.com/ClickHouse/clickhouse-docs/blob/main/docusaurus.config.js
• If adding a new integration page, also add an entry to the integrations list here: https://github.com/ClickHouse/clickhouse-docs/blob/main/docs/en/integrations/index.mdx

[justindeguzman]

Thanks @Blargian. I'm going to merge this in as an improvement, but my suggest would be to:

• Flip the menus so that the top-level categories are the first menu, and the second menu opens the navbar for the current category
• For the top-level menu, it maybe should not be an icon but instead "Getting Started", "Cloud", etc. The double menus may look confusing

[Blargian]

Thanks @Blargian. I'm going to merge this in as an improvement, but my suggest would be to:

• Flip the menus so that the top-level categories are the first menu, and the second menu opens the navbar for the current category
• For the top-level menu, it maybe should not be an icon but instead "Getting Started", "Cloud", etc. The double menus may look confusing

Thanks @justindeguzman, that makes sense. I'm thinking now maybe just a change to the styling of the menu you implemented for mobile is required:

The secondary menu on mobile could show the categories: Getting started, Cloud, Managing Data etc and instead of the sub-menu popping up on hover, it could slide out from the left of the screen or something.

I'll see what can be done.