Allow customized search URL for cell "Get Help" "search on" option

[hwine]

Currently, the provider for the "search on" item in the cell's "Get Help" menu is hardcoded to "google". For various reasons, not everyone wants to use Google, and the search URL format is "standardized" across providers.

Ideally, Marimo would use the browser's configured search engine (if feasible). Otherwise, a configuration item for this would be handy.

As an occasional user of Marimo, I don't know how open developers are to this sort of feature request, so I'm opening as a discussion first.