fix(backend): make operation timeouts configurable

[grassiale]

Fixes #2410

On large clusters (e.g. AWS MSK with thousands of partitions and IAM authentication), the hardcoded 6s timeout in GetClusterInfo and 5s timeout in GetTopicsOverview lead to errors such as "context deadline exceeded" and broken broker connections.

This patch introduces a new OperationTimeouts config block under console.operationTimeouts with clusterInfo and topicsOverview duration fields. The original values (6s / 5s) are default.

Example configuration:

  console:
    operationTimeouts:
      clusterInfo: 30s
      topicsOverview: 30s

I'm not sure if the configuration should be under console or under kafka