Adds support for exporting to OpenSearch

[wild5r]

here is support for exporting to OpenSearch. The current integration with ElasticSearch was not compatible with the latest version of OpenSearch, despite the APIs being roughly similar

[fhamborg]

Thanks for the PR. Already with previous additions of export capabilities to more and more 3rd party systems, I had the thought that plainly adding all these individual systems to NP's export may at some point in time lead to a non-optimal situation. Specifically, I'm worried about having all these dependencies in setup.py and requirements.txt as well as the code additions requiring maintenance - whereas most users either don't use any of them or if at all only one.

Now adding another one, which is even just a variant of one that is already supported by NP (and AFAIK not hugely popular in comparison), raises theses thoughts even more so. I'm thinking that NP should probably come without any export functionality aside from JSON export and instead export functionality should be added

1. either using pip extras (such as, pip install news-please[opensearch])
2. or individual pip packages (such as, pip install news-please news-please-opensearch)

Excited to hear what the community thinks about this.

[wild5r]

Optionally, we can adapt the export to JSON for use with any ingestion tools like Beats, Logstash, and so on. This way, we can remove the code for some exporters and add examples of configuring ingestion tools to the documentation.