Put a Package/ID search box on the osv.dev main page

**Is your feature request related to a problem? Please describe.**
There is no search box present on the front page of `osv.dev`. In order to search `osv.dev`, you have to click on "Search Vulnerability Database", then click on the search box, then type your query. This requires two extra mouse clicks plus a page / screen change, which is excessive for such a core function of the website.

**Describe the solution you'd like**
There should be a package / ID search box on the main page of `osv.dev`, which functions identically to the one on `osv.dev/list`. (i.e. when a search query is submitted, the page redirects to `osv.dev/list`).

The search box should be brought into focus immediately when the page is loaded. This means the user can type or paste a query into the search box without having to manually click (or tab) to bring it into focus. (An example is when you visit [google.com](https://www.google.com)).

As an extra bonus, the search box on `osv.dev/list` should also be autofocused when the page is loaded.

**Describe alternatives you've considered**
Implement URL redirection so that navigating to `osv.dev/` redirects to `osv.dev/list` and performs a search for ``. This would be even more efficient, bypassing the main page completely, however this way of searching is less discoverable for a new user.

**Additional context**
Having search functionality immediately available on the main page would greatly improve the usability and discoverability of the OSV search function, which I think is one of the primary functions of the osv.dev website.