Add session argument in ShopifyApp::WebhooksManager.destroy_webhooks

[m11o]

What this PR does

Closes: #1568
When ShopifyApp::WebhooksManager.recreate_webhooks! is executed, it occurs bellow error.

session = ShopifyAPI::Auth::Session.new(shop: 'example.myshopify.com', access_token: 'access_token')
ShopifyApp::WebhooksManager.recreate_webhooks!(session: session)

ArgumentError (missing keyword: :session):
/vendor/bundle/ruby/2.7.0/gems/shopify_api-12.2.1/lib/shopify_api/webhooks/registry.rb:99:in `unregister'
/vendor/bundle/ruby/2.7.0/gems/sorbet-runtime-0.5.10324/lib/types/private/methods/call_validation.rb:157:in `bind_call'
/vendor/bundle/ruby/2.7.0/gems/sorbet-runtime-0.5.10324/lib/types/private/methods/call_validation.rb:157:in `validate_call'
/vendor/bundle/ruby/2.7.0/gems/sorbet-runtime-0.5.10324/lib/types/private/methods/call_validation.rb:89:in `block in create_validator_slow'
/vendor/bundle/ruby/2.7.0/gems/shopify_app-21.1.1/lib/shopify_app/managers/webhooks_manager.rb:33:in `block in destroy_webhooks'
/vendor/bundle/ruby/2.7.0/gems/shopify_app-21.1.1/lib/shopify_app/managers/webhooks_manager.rb:32:in `each'
/vendor/bundle/ruby/2.7.0/gems/shopify_app-21.1.1/lib/shopify_app/managers/webhooks_manager.rb:32:in `destroy_webhooks'
/vendor/bundle/ruby/2.7.0/gems/shopify_app-21.1.1/lib/shopify_app/managers/webhooks_manager.rb:22:in `recreate_webhooks!'

I think the reason the error occurred is ShopifyApp::WebhooksManager.recreate_webhooks! calls destroy_webhooks in it and calls ShopifyAPI::Webhooks::Registry.unregister in destroy_webhooks method.
But, destroy_webhooks doesn't receive any arguments, and it doesn't pass a session argument to unregister method.

So, This PR adds a session argument in destroy_webhooks method and passes it in recreate_webhooks!
Also, I add tests for destroy_webhooks because there aren't tests.

Things to focus on

1. lib/shopify_app/managers/webhooks_manager.rb

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.

Please review them.
Thanks

[dasmodal]

That looks good!

[klenotiw]

Yeah this looks great! Thanks so much for the contribution. If you can rebase and fix the conflicts we would love to get this in the next release.

[m11o]

@klenotiw
I fixed the conflict. Would you please review it?

[klenotiw]

Thanks for the contribution! 🎉