Fix connection pool math in Spring example config comments

[michaelraney]

Summary

• Corrected the connection pool math comment in the Spring example's keyspaces-application.conf
• Previous comment assumed 3 endpoints (VPC scenario) but the config connects to the public endpoint which exposes 9 peers
• Updated to reflect correct public/VPC endpoint counts and aligned with the documented best practice of 500 requests/sec per connection

What Changed

The comment block above advanced.connection.pool.local.size = 3 previously stated:

# If pool.local.size = 3 * 3 endpoints = 9 total connections for session
# For 9 connections at 3000 request per connection for a total of 27,000 rps

Updated to:

# Public endpoints expose 9 peers: pool.local.size = 3 * 9 endpoints = 27 connections.
# VPC endpoints typically expose 2-5 peers (most commonly 3).
# At 500 requests/sec per connection (recommended), 27 connections support 13,500 rps.

References

• Optimize client driver connections
• VPC endpoint connections