TCP connections to Milvus grow without bound when TLS is on #1034

Describe the bug:

Against a Milvus with TLS enabled, Attu's TCP connections to the Milvus proxy grow steadily and are never closed.

In our deployment, with a cluster page left open in a browser tab, the proxies held about 590 established connections from the single Attu pod. The count grew by about one per minute, matching the new Connect / GetVersion / CheckHealth sequence the proxy received from Attu each minute. With TLS off, the count stays flat.

The cause is in @zilliz/milvus2-sdk-node, which Attu v3.0.1 ships (3.0.6, with @grpc/grpc-js 1.14.4). When the SDK's channel pool destroys a client, it calls client.close() and then client.getChannel().getConnectivityState(true). On the closed channel, grpc-js then dials a new connection that nothing closes. With TLS each of these is a separate socket. Without TLS grpc-js reuses one socket, which hides the leak.

Fix PR in the SDK: milvus-io/milvus-sdk-node#615

It would help if Attu bumped the SDK once that fix is released. Reusing one client instead of opening a new connection every minute would also avoid the churn.

Steps to reproduce:

1. Run Attu v3.0.1 against a Milvus with TLS on (common.security.tlsMode: 1).
2. Open a cluster page and leave the tab open.
3. Count established connections to port 19530 from the Attu pod on the Milvus proxy (e.g. /proc/net/tcp6 in the proxy container). It grows by about one per minute and never drops.

Attu version:
v3.0.1 (zilliz/attu:v3.0.1)