Implement migration to opensearch
This is an attempt to implement #40 (closed):
- I reverted the changes related to the migration from ElasticSearch 7 → 8
- I reintroduced some typings
This works locally for some basic requests.
Before going further, I would like to know your opinion on that move @chocobozzz? Should we consider supporting OpenSearch only? Or OpenSearch + ElasticSearch? Or you'd like to stick with ElasticSearch?