Define a `type` property and value when creating an experiment

[jaredcobb]

A recent change to the required properties on the Experiment JSON object has broken the ability to create experiments. See https://developers.optimizely.com/x/rest/v2/#Experiment_ there is now a property named type that is required and the plugin doesn't take this into account.

The experiment data payload is defined here

wordpress-optimizely-x/includes/class-ajax-metabox.php

Lines 358 to 383 in ef3a6c1

	// Build the data array for the experiment.
	$experiment = array(
	'metrics' => array(
	array(
	'aggregator' => 'unique',
	'event_id' => absint( $event_id ),
	'scope' => 'visitor',
	),
	),
	'name' => sprintf(
	/* translators: 1: post ID, 2: post title */
	esc_html__(
	'WordPress [%1$d]: %2$s',
	'optimizely-x'
	),
	absint( $post->ID ),
	esc_html( $post->post_title )
	),
	'project_id' => absint( $project_id ),
	'status' => 'paused',
	'variations' => $this->generate_variations(
	$variations,
	$targeting_id,
	$post
	),
	);

and needs to add the type property. The value should be defined based on how many variations were created by the user.

Three or fewer variations should be an a/b value (2 variations and the original) else it should be multivariate.