Show alert on confirmation for large transaction amounts

#Description
As a user, I want to be alerted if I an submitting a large value transaction so I don't accidentally send a unintentional large amount

#Situation
GIVEN: I am confirming a transaction (transaction confirmation, approve, etc)
WHEN: When I submit a transaction that is a duplicate of another transaction
THEN: I should get an alert notifying me that it is a duplicate transaction

*Questions
- What would be considered a large amount? Over $1k, 10k?

[Error use cases](https://docs.google.com/spreadsheets/d/195Vw7sJcAeIzJFrpH1mE7MNVtb8tyPTJXADUvv4GQ3A/edit#gid=0)

The issue concerns the transaction confirmation flow in the MetaMask browser extension, but it names no files, tests, or entry points. First resolve whether the alert is for duplicate transactions or large amounts, define the threshold and supported confirmation types, then identify the relevant confirmation code and tests before implementation.

Written by the indexing model from the issue text.