Fix exchange rate issue with automated invoicing in qbo

[renintw]

In the 2017 discussion mentioned in the issue, it can be seen that at that time, even if you didn't provide an exchange rate when calling the QBO API, QBO would automatically fill in the exchange rate for you. So I tested in this direction in the first place but then found that if you don't include the ExchangeRate in the API call now, QBO will automatically set the value to 1: "CurrencyRef":{"value":"EUR","name":"Euro"},"ExchangeRate":1.

After searching, I found discussions indicating that the QBO invoice API does not support automatically providing the ExchangeRate (perhaps they changed the rules at some point after 2017). You have to get the value yourself and include it in the payload. So here I used the get exchange rate API also from QBO (the sample on the page doesn't work, but the API actually works..).

In addition, the local QBO connection is also fixed. It turned out that the relevant SDK was missing, and installing it solved the issue.

Fixes #1250

Screenshots

Exchange rate now correctly displays

	Invoice manually created in QBO	Invoice sent from WordCamp
EUR
JPY

How to test the changes in this Pull Request:

1. composer update.
2. Follow https://github.com/WordPress/wordcamp.org/tree/production/public_html/wp-content/plugins/wordcamp-qbo#wordcamp-qbo to set up QBO locally.
3. Add a new sponsor invoice here in /wp-admin/post-new.php?post_type=wcb_sponsor_invoice.
   • If the community dropdown does not display any country options, click on "Delete Cache" and then refresh.
4. Approve the invoice you added in /wp-admin/network/admin.php?page=sponsor-invoices-dashboard&section=submitted
5. Go to https://app.sandbox.qbo.intuit.com/app/invoices and enter the invoice editing screen.
6. Check if exchanges are correct. (you can test with multiple currencies)

[pkevan]

unsure if this is debugging code left in or needed?

[renintw]

This code appears in other parts as well. You can see logs on the terminal and can also check them using wp wc-misc format-log wp-content/debug.log as specified in the QBO Readme.

[renintw]

It appears that it can also let you see the production logs. (ref)

[pkevan]

ok - but it's kind of pointless logging every time we do a lookup isn't it?

[renintw]

I don't feel strongly about it; just following the practice here. Perhaps there was a discussion that every API call should have a logger and what benefits it would bring? I'm not sure. However, removing it here makes sense to me since it isn't a critical call. What do you think?