5325: Documents database stats r=irevoire a=ManyTheFish
# Pull Request
## Related issue
Fixes#5319
## List
- Create a DatabaseStats struct
- Compute and store the documents database stats in the IndexStats
- Force dumpless upgrade to update the index stats
- when a document addition/modification/deletion is made, we only recompute the database stats on the added/modified/deleted documents
Co-authored-by: ManyTheFish <many@meilisearch.com>
Co-authored-by: Many the fish <many@meilisearch.com>