Add search to pkgdown for Connect API

[fh-mthomson]

While trying to interact with the Connect API, I often reference:

1. connectapi pkgdown: https://pkgs.rstudio.com/connectapi/
2. Connect app docs: https://docs.posit.co/connect/cookbook/

Two requests to make this slightly easier to find the relevant information:

1. Add Search functionality to the connectapi pkgdown site
2. Add Filter to Connect docs to limit search results to ONLY the API Cookbook and/or API Reference.

Motivating example: If I want to search for a specific endpoint name, I don't always want to see user-facing docs.

Thanks for the consideration!