[Contributor] I want participate as contributor #82
Description
Hello I've been working with your code and I have some improvements that I believe could be valuable for the community.
In my environment, Elasticsearch is not directly exposed, and we do not have Kibana to help, so we need to connect through an API Gateway (here we use Gravitee), which requires using X-API-Key as an authentication method.
We also rely heavily on Mustache templates. So, this extension makes perfec sense, and will help us a lot.
Here are the changes I made:
1 - Improve verbose logs
2 - Added support for extra request headers (e.g., X-API-Key).
3 - Added support for complex Mustache templates, including JSON validation and correct request handling to Elasticsearch.
Please let me know if I can create a branch and submit a Pull Request for your review.