chore: [DX-3334] Add the Subresource Integrity attribute to Checkout files

[zaidarain1]

Fixes a security issue with checkout widgets where there were no integrity checks for the widgets files being downloaded from jsdelivr to ensure they weren't tampered with.

Changes:

• In the PR workflow, if the widgets library package has changed and the new build output hashes havent been commited, the workflow will fail and instruct on how to update the hashes
• Before downloading either the widgets-esm or widgets.js files, ensure their integrity with their hash
• Push a hashes.json file that will be the source of truth for valid hashes

[nx-cloud]

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✅ Successfully ran 4 targets

• nx run @imtbl/checkout-widgets:build
• nx affected -t build,lint,test,typecheck
• nx run @imtbl/sdk:build
• nx run-many --target=build --projects=@imtbl/sdk

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