[Cashtab] [chronik tx history p2] Add a function to combine chronik tx history for all addresses into a single array

Summary:
T2447

Depends on D12048

Add a function to combine the API output of chronik.script.history called on all addresses into a single array

Test Plan:
Review the unit test, mocks
npm test

npm start
Observe in dev console that chronikTxHistory as flattened array includes all the tx entries from txHistoryOfAllAddresses

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D12051