Update config and fix config naming.

[thruflo]

Support:

electric config update [--app APP] [--env ENV] [--migrations-dir PATH]

Fix naming to use app and env everywhere, including the electric.json. And update the README to match latest usage.

[thruflo]

Messed up the last commit: the "bump the version" commit actually also makes a breaking change to the bundle format to get rid of the named data import, so rather than:

import { data as bundle } from '../migrations/dist'

We just have:

import bundle from '../migrations/dist'

[icehaunter]

Please add Closes VAX-### into the PR body

[thruflo]

Closes VAX-###

Relates to [VAX-518] but doesn't close it without other PRs across repos.