Fix caching for GraphQL queries

[alecgeatches]

We currently use this HTTP caching strategy on trunk:

remote-data-blocks/inc/Config/Query/HttpQuery.php

Lines 43 to 48 in 4f6e62a

	// For most HTTP requests, we only want to cache GET requests. This is
	// overridden for GraphQL queries when using GraphqlQuery
	if ( 'GET' !== strtoupper( $this->get_request_method() ) ) {
	// Disable caching.
	return -1;
	}

The comment is incorrect. We inherit the same strategy in GraphqlQuery, and this has some issues. GraphQL queries are typically implemented as POST requests, which means that we're skipping the cache each time we make a GraphQL query. For large pages of items or a lot of properties, this results in a huge number of cache misses and slow page loads for our GraphQL data sources like Shopify.

This PR adjusts GraphQL queries to use the default caching strategy, ignoring the fact that it's a POST request. GraphQL mutations are still uncached.

Testing

1. On the trunk branch, set up a Shopify connection.

2. Create a new post and add a product with the default template.

3. Publish the page and view the page on the frontend as a logged-in user (e.g. as admin on a local wp-env instance).

4. View the Query Monitor logs by clicking on the query monitor bar (top arrow) and clicking the "Logs" tab on the lower left:

   

5. Note the several logs related to cache misses. Refresh the page and confirm that caching is not working.

6. Switch to this branch fix/graphql-caching.

7. Refresh the page. You should see one cache miss follow by several cache hits:

   

8. Refresh again. All requests should hit the cache now, and the page should load very quickly.

9. Wait 60 seconds and refresh. You should see a fresh uncached request followed by cached result, the same as step 7.

[github-actions]

Test this PR in WordPress Playground.

[shekharnwagh]

Works as described. Thank you for fixing it !

[alecgeatches]

Thank you @shekharnwagh! Merging!