Fix engine initialization

[kirillplatonov]

What this PR does

ShopifyApp engine initialization is broken in v23.0. I couldn't launch the app after update because of error:

➜  color-swatches git:(main) ✗ bin/rails test
/Users/kirill/.local/share/mise/installs/ruby/3.4.5/lib/ruby/gems/3.4.0/gems/shopify_app-23.0.0/lib/shopify_app/engine.rb:28:in 'block (2 levels) in <class:Engine>': uninitialized constant ShopifyApp::Engine::WebhooksManagerJob (NameError)

          WebhooksManagerJob.log_arguments = false
          ^^^^^^^^^^^^^^^^^^

This PR delays job params customization until initialization is complete and zeitwerk already loaded job classes.

Checklist

Before submitting the PR, please consider if any of the following are needed:

• Update CHANGELOG.md if the changes would impact users
• Update README.md, if appropriate.
• Update any relevant pages in /docs, if necessary
• For security fixes, the Disclosure Policy must be followed.

[kirillplatonov]

Hi @lizkenyon,
Could you please review this PR?

[lizkenyon]

hi @kirillplatonov TY for this! ⭐

Looks like we handle this in our app template. But solving it here is a much more robust solution.