Improve indexing speed

**Motivation**
The events-metrics routine seems a lot faster than the projections linked to Elasticsearch views.

This is likely related to the SQL query as the second one has to incorporate tombstones.

There may be to handle indexing with tombstones in a faster way than with using a UNION

**Acceptance criteria**
1. The reindexing process should get faster
2. It has no impact on the result