Support for basic filtering of collections e.g. only indexing published posts

[willbrowningme]

The addon is brilliant so thank you for creating it.

It would be great to add basic filtering on collection fields so that you can choose to only index certain items in a collection.

For example if you have a collection of blog posts you might not wish to index posts that are currently drafts and have not yet been published as they could then appear in any search queries.

Perhaps doing something like this in config.yaml

detektivo:
    engine: algolia
    app_id: <APP-ID>
    api_key: <API-KEY>
    collections:
        posts: [published:true, title, excerpt, content]

I updated a couple of files to get the above config.yaml working for my use case however the implementation isn't great.

In Controller/Admin.php update the foreach loop in the reindex method on line 33

foreach ($fields as $field) {
    $parts = explode(':', $field);
    $field = $parts[0];

    $options['fields'][$field] = 1;

    if(isset($parts[1])){
        $filter = $parts[1];

        if($filter == 'true'){
            $filter = true;
        } else if($filter == 'false'){
            $filter = false;
        }

        $options['filter'][$field] = $filter;
    }
}

In bootstrap.php update the foreach loop in 'collections.save.after' on line 78

foreach ($fields as $field) {
    $parts = explode(':', $field);
    $field = $parts[0];

    if (isset($entry[$field])) {
        $data[$field] = $entry[$field];

        if(isset($parts[1])){
            $filter = $parts[1];

            if($filter == 'true'){
                $filter = true;
            } else if($filter == 'false'){
                $filter = false;
            }

            if($entry[$field] !== $filter){
                return;
            }
        }
    }
}

Now whenever reindexing or saving a blog post if you have set published:true in your config.yaml only published posts will be indexed with your Detektivo engine (in my case Algolia).

This seems to work with simple filtering like the below but the implementation could definitely be improved.

posts: [published:true, title:Example Post, excerpt, content]