Add tools for generating a simulated Payment History for testing (replaces #4655)

[willy-b]

• Submitted a ticket for my issue if one did not already exist. This fixes Sample Ledger data files (ledger-*.json) for testing & development? #4199 .
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).

Adds npm script: npm run add-simulated-payment-history

This generates a simulated Payment History, allowing testing of features that depend transactions without spending BTC or waiting.

Also tools/lib/transactionHelpers.js has a few functions for generating randomized transaction data (with constraints if you like) and a general transaction validator (using Joi).

fixes #4199

Test Plan:

1. Clear user data (npm run clean userData)
2. Start Brave
3. Enable Brave Payments
4. Observe no transactions, empty wallet, Payment History link is unavailable
5. Run npm run add-simulated-payment-history
6. Switch to Brave and Toggle Payments
7. Observe Payment History link is available
8. Open Payment History.
9. Observe 10 months of randomized Payments data
10. Open /\<UserDataPath\>/ledger-state.json and confirm transactions are present

[diracdeltas]

++