Migrate ADX operator federation Kusto data-plane usage to azkustodata

[mkeesey]

Context

The ADX operator still uses the legacy github.com/Azure/azure-kusto-go/kusto data-plane client for federation, heartbeat, and hub artifact reconciliation.

This is separate from the ARM management client usage, which already uses armkusto and is not in scope.

Files

• operator/adx.go
• operator/adx_test.go

Current legacy usage

• Creates data-plane clients with kusto.NewConnectionStringBuilder and kusto.New.
• Uses default credential and user-assigned managed identity auth through the old connection string builder.
• Executes management commands with legacy client.Mgmt.
• Executes heartbeat table queries with legacy client.Query.
• Builds statements with legacy kusto/kql.
• Reads rows with NextRowOrError and ToStruct.

Major paths to migrate

• ensureHeartbeatTable: .show tables | count, .create table.
• HeartbeatFederatedClusters / heartbeatFederatedCluster: schema collection and heartbeat ingestion.
• Schema discovery: .show databases, .show database schema, .show functions, .show function <name> schema as json.
• Heartbeat ingest: .ingest inline into table.
• FederateClusters: reads heartbeat rows and reconciles hub artifacts.
• Hub artifact reconciliation: hub tables, entity groups, .execute database script, .create-or-alter function.

Acceptance criteria

• Operator production code no longer imports github.com/Azure/azure-kusto-go/kusto... packages.
• Federation heartbeat send/read behavior remains covered by tests.
• Hub table, entity group, and generated function reconciliation continue to work.
• ARM armkusto provisioning code remains unchanged except where needed to keep interfaces clean.