Add expiring offline token support

[zzooeeyy]

What this PR does

• https://github.com/shop/issues-app-access/issues/791

Depends on new shopify-api-ruby version with this change:

• Add expiring offline access token support shopify-api-ruby#1423

Reviewer's guide to testing

Adds support for expiring offline access tokens with automatic token refresh for apps using ShopSessionStorage.

📖 See Migration Guide for setup instructions.

Key Changes

• ShopSessionStorage automatically refreshes expired tokens in with_shopify_session (Overwritten from SessionStorage concern) (default behaviour)
  • Added refresh_token_if_expired! public method for manual token refresh
• ShopSessionStorage now automatically store session attributes (access_scopes, expires_at, refresh_token, refresh_token_expires_at)
• UserSessionStorage now automatically store session attributes (access_scopes, expires_at)
• Deprecated ShopSessionStorageWithScopes and UserSessionStorageWithScopes (to be removed in v23.0.0)
• Shop model generator prompts for migration to add expires_at, refresh_token, and refresh_token_expires_at columns
• Documentation includes migration guide with background job example for migrating existing shops using ShopifyAPI::Auth::TokenExchange.migrate_to_expiring_token

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.