make max open connections configurable for ch

[iuwqyir]

TL;DR

Added support for configuring the maximum number of open connections to Clickhouse.

What changed?

• Added a new MaxOpenConns field to the ClickhouseConfig struct in configs/config.go
• Modified the Clickhouse connection setup in internal/storage/clickhouse.go to use the configured MaxOpenConns value when it's greater than 0

How to test?

1. Set the maxOpenConns parameter in your Clickhouse configuration
2. Verify that the connection pool respects this limit under load
3. Monitor Clickhouse server connection metrics to confirm the limit is enforced

Why make this change?

This change allows for better control over connection pooling to Clickhouse, which can help prevent connection exhaustion under high load. By limiting the maximum number of open connections, we can ensure the application doesn't overwhelm the database server with too many concurrent connections, improving stability and resource utilization.

[iuwqyir]

• make max open connections configurable for ch #188 👈 (View in Graphite)
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