[Cashtab] [chronik tx history p9] Correctly calculate etoken amount for genesis txs

Summary:
T2447

Depends on D12089

Correctly calculate minted amount for eToken genesis txs

Note: still need to correct these amounts for etoken decimals, will happen in another part of this stack

Test Plan:
Review unit test and npm test
Mint an eToken and confirm the eTokenAmount field is correct (although it is not adjusted for decimal places)

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D12129