[Feature] Support for Unified Host

[tanmay-db]

What changes are proposed in this pull request?

This PR adds support for unified host:

• Separates client type from host type determination, deprecating isAccountClient and replacing it with getHostType() and getClientType() methods using new HostType and ClientType enums
• Adds an experimental flag to indicate if a host is unified: experimentalIsUnifiedHost
• Adds a workspaceId attribute to DatabricksConfig, which is necessary for workspace clients that talk to unified hosts
• Adds getUnifiedOidcEndpoints() function, which is used in the OIDC endpoint resolution logic to discover OAuth endpoints on unified hosts
• Adds header injection logic in DatabricksConfig.authenticate() which adds an X-Databricks-Org-Id header to requests made by workspace clients on unified hosts
• Adds comprehensive test coverage including unit tests for host/client type detection, OIDC endpoint resolution, header injection, and integration tests

Similar to what is done for:

• databricks/databricks-sdk-py#1135
• databricks/databricks-sdk-go#1307

How is this tested?

• Unit tests
• Manually E2E tested with a spog profile

[github-actions]

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Trigger:
go/deco-tests-run/sdk-java

Inputs:

• PR number: 612
• Commit SHA: 129448613115c41312cd607da14cbeb6b2c04f6a

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