Display sync history

[JakePT]

Description of the Change

Displays the sync history on the sync page. Currently limited to Completed syncs (with errors or not).

How to test the Change

• Visit ElasticPress > Sync. A Sync history panel should be visible with at least one previous sync (if coming from < 5.0.0).
• When a new sync is completed it should be added to the list automatically without a refresh.
• If a a sync is triggered via WP CLI that should be reflected in the the sync title.
• The history should not appear for the initial sync on a site, or after deleting an index.
• The Delete and sync... and Advanced options panels should only be visible if there is a sync history.

Changelog Entry

Added - Added a sync history to the Sync page.

Credits

Props @JakePT @felipeelia @brandwaffle @anjulahettige Apurv Ray

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests pass.

[felipeelia]

@JakePT I gave this a try and it seems we are not capturing if a sync failed or not. Adding this snippet to a mu-plugin makes the [illegal_argument_exception] Limit of total fields [5000] in index [elasticpresstest-post-1] has been exceeded error to happen:

add_filter(
	'ep_prepare_meta_data',
	function( $post_meta, $post ) {
		for ( $i = 0; $i < 100; $i++ ) {
			$post_meta[ "test_meta_{$i}_title_{$post->ID}" ] = 'Lorem';
			$post_meta[ "test_meta_{$i}_body_{$post->ID}" ]  = 'Ipsum';
		}
		return $post_meta;
	},
	10,
	2
);

I can see the errors in the log. If I wait for it to complete and reload the page I can see the new entry but it says it was successful.

[felipeelia]

@JakePT we talked about this and it is enough to say it was triggered due to a setting change, we do not need to specify the change for now.