Better defaults in v1.26

[etiennedi]

Over time, we've learned how users use Weaviate and which settings fit most use cases. Based on those learnings we want to improve default values as follows:

• [HNSW] Reduce default maxConnections from 64 to 32 #4363
• Discussion: Better sharding defaults when replication is used. #4473
• DB access patterns: Make pread the default (instead of mmap) #4464