feat(lakebase): add Lakebase Vector backend

[junyulabs]

Summary

This PR adds Lakebase Vector backend to VectorDBBench.

Usage

To run the Performance768D100M workload on Neon:

1. Create a Neon instance with 40 CUs and wait until it is ready.
2. Enable the Lakebase Vector extension by https://neon.com/docs/extensions/lakebase-vector
3. Install and run VectorDBBench

export POSTGRES_HOST="<POSTGRES_HOST>"
export POSTGRES_PASSWORD="<POSTGRES_PASSWORD>"
export NUM_PER_BATCH=10000

vectordbbench lakebaseann \
  --host $POSTGRES_HOST \
  --user-name neondb_owner \
  --db-name neondb \
  --table-name vdbbench_laion100m \
  --db-label lakebase-search-laion100m \
  --task-label lakebase-search-laion100m \
  --case-type Performance768D100M \
  --k 100 \
  --load-concurrency 1 \
  --num-concurrency 1,5,10,20,30,40,60,80,100,120 \
  --concurrency-duration 30 \
  --concurrency-timeout 3600 \
  --max-parallel-workers 95 \
  --drop-old \
  --load \
  --search-concurrent \
  --search-serial \
  --probes 54,380 \
  --epsilon 3.2

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[junyulabs]

/assign @XuanYang-cn