Create entity browser upload plugin for media entity images

Note: An embed plugin got added in July. That being said, it's laking most of the configuration options in the Entity Browser creation UI, which makes it a bit hard to use.

Working on fixing that as a first step, so assigning myself. Patch coming up soonish.

Had to take an unexpected break, so it took a bit longer than planned, but here it is.

I'm still wondering about a few things in this patch though:

1. Not sure about what would be best in case 0 ; current action match Entity Browser "your view is incorrectly configured, go fix it" behavior, and makes the site builder next step obvious, but I'm not sure having them lose the configuration of the entity browser in the process might not be ideal.
2. Left the current "upload path" configuration in place ; not sure that's a good idea though, defaulting to the path set in the source field is probably better for most workflow

Thought about those two points more than welcome.

(Sidenote: also converted two remaining t() call to $this->t() , thought it wasn't worth it's own dedicated issue, but can be split if you want)

Looks like it was late on Friday, not sure how I missed the fact that the source field type was a property of the media bundle… Replaced the loadMultiple by a loadByProperties, which will avoid loading bundles unnecessarily.

Also thought a bit more about the first point during the week-end, and maybe the correct fix would be to expand EntityBrowser WidgetInterface slightly, adding a method to check if a specific plugin should be available or not in the list based on the current site configuration. The View widget could use it to hide itself if there's no view with an entity_browser_display available, and ME image upload plugin could hide itself if there's no image bundle.