Re-add deprecated files to prevent major release

[paulomarg]

What this PR does

In #1861, we (correctly) removed some files related to JWT that should no longer be used in shopify_app. However, by removing those files we'd be forced to make a major release, which is still a bit too close to the last one.

This PR adds back the code that was removed (but will be unused internally) so it doesn't break existing apps. It will log deprecations for them instead.

Log message will look like this

================================================
=> Upcoming deprecations in v23.0:
* 'CallbackController::perform_after_authenticate_job' and related methods 'install_webhooks', 'perform_after_authenticate_job'
* will be removed from CallbackController in the next major release. If you need to customize
* post authentication tasks, see https://github.com/Shopify/shopify_app/blob/main/docs/shopify_app/authentication.md#post-authenticate-tasks

* ShopifyApp::JWTMiddleware will be removed, use ShopifyApp::WithShopifyIdToken instead.
================================================

Reviewer's guide to testing

Use this branch in the Gemfile of an app using the ruby template, and set it up to use ShopifyApp::JWTMiddleware.

Things to focus on

1. Is it ok to not have tests? The feature will be unchanged until the next major release.
2. Can you see any fringe cases where it won't work?

[joevandyk]

is there a way to silence these log messages? i'm installing shopify_app in a brand new app, and these messages don't seem terribly useful.

[paulomarg]

Fair question! I'll add that to our tracking to see if we can hide these warnings based on the package version.

For the sake of transparency, we might not get to this immediately though.