configs for http connections

[youngyjd]

What changes were proposed in this pull request?

Added configurable HTTP connection pool settings for Gravitino Java client:

• New configs: gravitino.client.maxConnections and gravitino.client.maxConnectionsPerRoute (default: 200)
• Updated HTTPClient to configure connection manager with these settings
• Updated GravitinoLanceNamespaceWrapper to pass client configs to GravitinoClient
• Added comprehensive unit tests (9 tests total across configuration and integration)

Why are the changes needed?

Apache HttpClient 5.x defaults to only 25 total connections and 5 per route, causing severe bottlenecks in high-throughput scenarios. With Lance REST server running 800 threads, requests queue for connections, resulting in P99 latency of 4 seconds.

Fix: #(issue)

Does this PR introduce any user-facing change?

Yes - Adds two new optional configuration properties:

• gravitino.client.maxConnections - Max total HTTP connections (default: 200, previously 25)
• gravitino.client.maxConnectionsPerRoute - Max connections per destination (default: 200, previously 5)

For Lance REST server users: Add these configs to gravitino-lance-rest-server.conf to tune performance.
Performance improvement: Default configuration now provides 8x more connections, significantly reducing latency out-of-the-box.

How was this patch tested?

• Added 5 unit tests in TestGravitinoClientConfiguration (defaults, custom values, validation, integration)
• Added 4 unit tests in TestHTTPClient (connection manager configuration, high-throughput scenarios)
• Added 6 unit tests in TestGravitinoLanceNamespaceWrapper (property extraction, filtering, edge cases)