Rename package to ShopifyCheckoutSheetKit

[cianbuckley]

What are you trying to accomplish?

Sorry. Renaming the kit to Shopify-Checkout-Sheet-Kit

• rename ShopifyCheckoutKit to ShopifyCheckoutSheetKit
• rename class files (main entry point, test, .podspec)
• rename SPM
• bump podspec version
• update all links in docs NOTE: Links will be broken until repo update!

essentially all searches of:

• CheckoutKit
• checkout-kit
• Checkout Kit

does not rename:

• CheckoutViewController
• CheckoutWebView
• CheckoutWebViewController

How to test

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Testing

• [x] I've added tests to support my implementation

Contribution guidelines

• [x] I have read and agree with the Contribution Guidelines.
• [x] I have read and agree with the Code of Conduct.

Documentation

• [x] I've updated any documentation related to these changes.
• [x] I've updated the README.

Versioning

• [x] I have bumped the version number in the .podspec file.
• [x] I have bumped the version number in the README.
• [] I have added a Changelog entry.

After merging

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