Add support for authentication through Azure MSI

[Divyansh-db]

Summary

Adds Azure Managed Service Identity (MSI) authentication to the Java SDK, porting the azure-msi credential strategy from the Go SDK (https://github.com/databricks/databricks-sdk-go/blob/main/config/auth_azure_msi.go).

Why

The Java SDK had the azureUseMsi config field (ARM_USE_MSI) wired up but no provider behind it. Users on Azure VMs, App Service, or Functions with managed identities had to fall back to service principal secrets or Azure CLI. The Go SDK has supported this since early on — this PR closes the gap.

What changed

Interface changes

• AzureMsiCredentialsProvider — New CredentialsProvider with auth type "azure-msi". Activated when isAzure() &&
  ARM_USE_MSI=true && (host or resourceId is set).
• AzureMsiTokenSource — TokenSource that fetches tokens from the Azure IMDS endpoint
  (http://169.254.169.254/metadata/identity/oauth2/token). Supports system-assigned and user-assigned identities (via ARM_CLIENT_ID).

Behavioral changes

• Default credential chain now includes azure-msi between azure-github-oidc and azure-client-secret, matching Go SDK ordering.
• Produces Authorization, X-Databricks-Azure-SP-Management-Token, and X-Databricks-Azure-Workspace-Resource-Id headers.

Internal changes

• MsiTokenResponse POJO for IMDS JSON deserialization (mirrors Go's msiToken struct), handling expires_on (epoch
  seconds).
• Null-safe isAzureUseMsi() helper for the boxed Boolean config field.
• Reuses AzureUtils.ensureHostPresent() for workspace URL resolution, consistent with other Azure providers.

How is this tested?

20 unit tests in AzureMsiCredentialsProviderTest across two groups:

• TokenSourceTests (12) — IMDS request shape, response parsing, table-driven client_id handling (3 cases),
  table-driven invalid responses (5 cases: missing fields, bad expiry), HTTP error paths.
• ProviderTests (8) — Mirrors Go SDK's TestMsiHappyFlow, TestMsiHappyFlowWithHostAndNoResourceID,
  TestMsiFailsOnResolveWorkspace, TestMsiTokenNotFound, plus table-driven null-return preconditions.

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Inputs:

• PR number: 760
• Commit SHA: 222a66e1ee3114585b4094f74264f7db521802db

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