feat: function search route

[hholb]

We have a couple of places on the frontend where it would be nice to have the ability to search through functions.

On the garden pages, we allow users to add existing functions to gardens:

And for superusers (and maybe other users someday) we have a simple component for selection functions to run benchmarks on:

In both of the cases it is a pain to find a specific function you are looking for. This will become more painful the more functions we have in the database. It would be nice to have a search route for functions similar to the /gardens/search route so we can facilitate a nicer way of finding specific functions on the frontend.

We already have most of the plumbing in place to do a nice function search. We already have a materialized view called modal_function_documents for vectorized full-text search through function metadata that we use when searching gardens. It shouldn't be too much of a lift to add a search route for functions that leverages this view and returns matching functions.