new custom instances of find, initial configuration

it would be nice to have a simple mechanism to make a custon config for a Find instance, to feed it with initial data (engines, symbols etc.).

Currently, Find as default browser search engine, should load only the `/src/index.js` file, because CSS and interface in JS are not needed, the user is "passing by" to its final URL destination. The browser has probably already cached all static assets, but we don't want to make a `fetch()` query every time the find pages load.

Therefore, the configuration of a custom instance should be "load(able/ed) by the user", without slowing "transient find executions" (also Find has no build pipeline).

Refs:
- https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes/rel/preload
- web workers