Make type param optional on webhook route

[lizkenyon]

What this PR does

Fixes Shopify Ruby Template , APP_UNINSTALLED Webhook Delivery Failed, Can't Verify CSRF Token.

• This makes the type param on the webhooks route optional
• When webhooks are initiated from the CLI they are sent to the /api/webhooks address
• Prior to this change this was causing CLI initiated webhooks to error
• The webhook type is never read from the URL param, and always from the webhook header so we do not forsee any issues with making this param optional.

Reviewer's guide to testing

Are there any cases where you forsee this being an error?

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.