Enforce new lines between import groups

[keyfer]

This enforces a new line between import groups, from this rule: https://github.com/benmosher/eslint-plugin-import/blob/master/docs/rules/order.md#newlines-between-ignorealwaysalways-and-inside-groupsnever

The reason I chose this approach is because it enforces what looks to be the side our codebase leans towards:

The effect of running with always (caps at 999)

The effect of running with never

With the addition of this rule the following are true:

Invalid

import fs from 'fs';
import path from 'path';
import index from './';
import sibling from './foo';

Valid

import fs from 'fs';
import path from 'path';

import index from './';

import sibling from './foo';

I attempted to see what this rule would cause if I also ran --fix on web, and this was the result:
https://github.com/Shopify/web/pull/18382

[BPScott]

LGTM. As discussed in Slack I think that always is nearer to what usually we try and do.

Work out what's going on with the tests and add a CHANGELOG entry before merging

[cartogram]

@keyfer seems like something is up those tests that is not related to this PR. I am going to take a look.

[cartogram]

@keyfer give this a rebase and I think you will be good to go.

[keyfer]

Thanks @cartogram