fix(payments-next): Show pre-discount tax

[xlisachan]

Because

• the post-discount tax amount is being displayed when we caveat that a discount will be applied when we should be displaying the pre-discount tax amount

This pull request

• Updates to display the pre-discount tax amount

Issue that this pull request solves

Closes: PAY-3635

Checklist

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• My commit is GPG signed.
• If applicable, I have modified or added tests which pass locally.

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