Add/switch feed v5

[message-dimke]

Changes proposed in this Pull Request:

Closes #833 .

Adds Pinterest API v5 integration into feeds.
Merging develop in as well to catch up on fresh phpcs and unit tests setups.

Detailed test instructions:

1. Checkout add/switch-feed-v5 branch.
2. Check Product Sync being at Settings tab.

3. Go to WooCommerce - Status - Scheduled Actions - Pending tab and force run pinterest-for-woocommerce-handle-feed-registration action.

4. Go to Pinterest and check for the feed to be present and active under Catalogues - Data Sources

• Feed name must be like "Created by Pinterest for WooCommerce [country(Site Language)]-[currency]."
• Feed must have Active Status

NOTE: Checks feed's Language column, it must be the same you have under your WordPress Settings.

5. Go to WordPress Settings and change Site Language to something else of your choice. I switched between US and UK English languages.

6. Check Pinterest Catalogues - Data Sources for another feed to be added and activated.

Changelog entry

Add - Pinterest API v5 feeds integration.

[message-dimke]

New v5 API does not have any analog of integration_platform_type for the feed which we are using to make sure we disable only feeds we created.

pinterest-for-woocommerce/src/FeedRegistration.php

Lines 233 to 236 in d41ee8e

	// Only disable feeds that are registered as WooCommerce integration.
	if ( 'WOOCOMMERCE' !== $feed->integration_platform_type ) {
	continue;
	}

[budzanowski]

I think that for now, we will need to operate based on the location only.

[budzanowski]

The addition of a develop merge will give us a nice base for full rebase.