Activate filtering programmatically

## Problem

I'm looking to enable filtering for my `github.com/charmbracelet/bubbles/list` component by default so that as soon as the list is rendered I can start to type, without needing to press the filter shortcut (`/`) first.

## Recreate

- Use the `list-default` example within the [charmbracelet/bubbletea](https://github.com/charmbracelet/bubbletea/blob/master/examples/list-default/main.go) repo
- Set `m.list.SetFilteringEnabled(true)` on line 82
- Note that this does not do anything

I'm relatively new to the package so I think this needs to be done at a different point within the model lifecycle, rather than at the point of creation. Any help would be great 👍