chore: improve plain releases for local builds

[doorgan]

Updates the just release-plain command to include a start_expertscript that takes care of wrapping the expert executable and pass the CLI flags correctly.

Also updates the docs nudging people to use plain releases when building expert from source.

The main idea here is that we make it easier and faster for users building expert from source (eg when developing) and reserve the cross platform burrito executables for the official releases that regular users download.

[doorgan]

I didn't like the default announcement message because it's misleading, you can't run expert with them and you can't pass cli flags to start or start_iex, so figured this way to replace it with a custom one.

[mhanberg]

I think we want all of these to show the full executable_path, for consistency.

[mhanberg]

why do we have this file and the one in overlays?

[doorgan]

Agh, there's a bug in the filetree plugin I use on neovim that would refuse to delete this file every time I moved it or renamed it. I forgot to remove this one again before committing

[mhanberg]

This would be a chore, not a feat

I think maybe it should be just release which does the plain release, just burrito does a burrito build for all platforms, and just burrito-local does a burrito of your local arch/os.

Will require changing the CD workflows