Update for Ember Octane / 4.x support

[gorner]

These updates are necessary to ensure compatibility with Ember Octane / 4.x. The main concern is updating ember-cli-babel to v7.26.11 since earlier versions of that lib referenced the Ember global and cause warnings to be thrown in any Ember 3.28+ app using it.

Note that while my working assumption is that this update should target master, the more useful diff here is likely 2.0.0-beta.1...gorner:octanify since I built off the https://github.com/gilgen/ember-pusher/tree/2.0.0-beta.1 branch, and the current master branch is actually v1.1.1. If you'd prefer that I create a v3 branch instead, let me know.

What else I've done:

• Updated the ember-cli blueprint to 3.28 - this includes a number of dependency updates and drops support for versions of Node before 12 (current Node LTS is v18)
• Updated code to explicitly inject the pusher service where necessary due to the removal of implicit injection support in 4.x (though leaving the initializer itself appears to be OK for now)
• Fixed a couple of other issues raised by the linter. In attempting to apply automated fixes for some of these, I ended up applying some code style updates from Prettier (included in the updated blueprint), I can revert these if you feel strongly about them.
• Moved the pusher-js package to a peer dependency - there've been several recent major-version bumps to pusher-js that don't impact ember-pusher so I don't think they need to be tightly coupled

However I haven't made any other significant changes to the add-on's structure or APIs.

If you have any other questions about this PR, you know where to find me 😉

[gilgen]

Nice. Thanks @gorner!