External Media: add toggle for feature in Jetpack settings

### Impacted plugin

Jetpack

### What

Jetpack is a multi-purpose plugin, so every feature it offers should be modular

### How

I'm creating this issue based on the discussion here: https://wordpress.org/support/topic/how-to-disable-the-menu-for-featured-images/

After installing Jetpack 14.3, I noticed a new menu with a few options when we click a post's featured image: https://d.pr/i/s6Ghar

I don't use and am not interested in any of those. Thus, Jetpack is making us click twice to get to the same place we used to get before with one click (WordPress' native media gallery). We should be able to disable this feature.

Start with the linked WordPress support discussion and the Jetpack 14.3 External Media menu shown in the issue. Trace where that menu and its Jetpack settings are registered, then compare existing feature toggles. Done means a setting can disable the External Media menu while leaving WordPress's native media gallery available.

Written by the indexing model from the issue text.