Add cloud field to HostMetadata (#710)

## 🥞 Stacked PR

- [**#710 Add cloud field to
HostMetadata**](#710)
[[Files](https://github.com/databricks/databricks-sdk-java/pull/710/files)]
- [#711 Fix GetWorkspaceClient for unified account
hosts](#711)
[[Files](https://github.com/databricks/databricks-sdk-java/pull/711/files)]
- [#712 Add test for GetWorkspaceClient with SPOG
host](#712)
[[Files](https://github.com/databricks/databricks-sdk-java/pull/712/files)]
- [#713 Call resolveHostMetadata on Config
init](#713)
[[Files](https://github.com/databricks/databricks-sdk-java/pull/713/files)]
- [#714 Resolve TokenAudience from host metadata for account
hosts](#714)
[[Files](https://github.com/databricks/databricks-sdk-java/pull/714/files)]
- [#718 Make GCP SA token refresh
non-blocking](#718)
[[Files](https://github.com/databricks/databricks-sdk-java/pull/718/files)]
- [#719 Add integration test for host metadata
resolution](#719)
[[Files](https://github.com/databricks/databricks-sdk-java/pull/719/files)]
- [#720 Remove unified flag usage, rely on host
metadata](#720)
[[Files](https://github.com/databricks/databricks-sdk-java/pull/720/files)]

---------
## Summary

Port of Go SDK
[#1512](databricks/databricks-sdk-go#1512).

Adds a `cloud` field to `HostMetadata` that is populated from the
`/.well-known/databricks-config` discovery endpoint.

**Why:** Today, `isAws()`, `isAzure()`, and `isGcp()` infer cloud type
by suffix-matching the workspace hostname against a hardcoded list of
known DNS zones. This works for standard deployments but fails for
non-standard hostnames (custom vanity domains, unified hosts, etc.). The
discovery endpoint is the authoritative source and already returns a
`cloud` field, but the SDK was discarding it.

**Changes:**
- `HostMetadata`: new `cloud` field (`@JsonProperty("cloud")`), getter,
and 4-arg constructor
- `HostMetadataTest`: deserialization with/without cloud, constructor
tests

`NO_CHANGELOG=true`

## Test plan
- [x] `HostMetadataTest`: 4 tests for cloud field deserialization and
constructors

Author: hectorcast-db

databricks-sdk-java/src/main/java/com/databricks/sdk/core/oauth/HostMetadata.java

@@ -20,6 +20,9 @@ public class HostMetadata {
   @JsonProperty("workspace_id")
   private String workspaceId;
 
+  @JsonProperty("cloud")
+  private String cloud;
+
   public HostMetadata() {}
 
   public HostMetadata(String oidcEndpoint, String accountId, String workspaceId) {
@@ -28,6 +31,13 @@ public HostMetadata(String oidcEndpoint, String accountId, String workspaceId) {
     this.workspaceId = workspaceId;
   }
 
+  public HostMetadata(String oidcEndpoint, String accountId, String workspaceId, String cloud) {
+    this.oidcEndpoint = oidcEndpoint;
+    this.accountId = accountId;
+    this.workspaceId = workspaceId;
+    this.cloud = cloud;
+  }
+
   public String getOidcEndpoint() {
     return oidcEndpoint;
   }
@@ -39,4 +49,8 @@ public String getAccountId() {
   public String getWorkspaceId() {
     return workspaceId;
   }
+
+  public String getCloud() {
+    return cloud;
+  }
 }

databricks-sdk-java/src/test/java/com/databricks/sdk/core/oauth/HostMetadataTest.java

@@ -0,0 +1,62 @@
+package com.databricks.sdk.core.oauth;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.junit.jupiter.api.Test;
+
+class HostMetadataTest {
+
+  private final ObjectMapper mapper = new ObjectMapper();
+
+  @Test
+  void testDeserializeWithCloud() throws Exception {
+    String json =
+        "{\"oidc_endpoint\":\"https://example.com/oidc\","
+            + "\"account_id\":\"acc-123\","
+            + "\"workspace_id\":\"ws-456\","
+            + "\"cloud\":\"aws\"}";
+
+    HostMetadata meta = mapper.readValue(json, HostMetadata.class);
+
+    assertEquals("https://example.com/oidc", meta.getOidcEndpoint());
+    assertEquals("acc-123", meta.getAccountId());
+    assertEquals("ws-456", meta.getWorkspaceId());
+    assertEquals("aws", meta.getCloud());
+  }
+
+  @Test
+  void testDeserializeWithoutCloud() throws Exception {
+    String json =
+        "{\"oidc_endpoint\":\"https://example.com/oidc\","
+            + "\"account_id\":\"acc-123\","
+            + "\"workspace_id\":\"ws-456\"}";
+
+    HostMetadata meta = mapper.readValue(json, HostMetadata.class);
+
+    assertEquals("https://example.com/oidc", meta.getOidcEndpoint());
+    assertEquals("acc-123", meta.getAccountId());
+    assertEquals("ws-456", meta.getWorkspaceId());
+    assertNull(meta.getCloud());
+  }
+
+  @Test
+  void testConstructorWithCloud() {
+    HostMetadata meta = new HostMetadata("https://example.com/oidc", "acc-123", "ws-456", "gcp");
+
+    assertEquals("https://example.com/oidc", meta.getOidcEndpoint());
+    assertEquals("acc-123", meta.getAccountId());
+    assertEquals("ws-456", meta.getWorkspaceId());
+    assertEquals("gcp", meta.getCloud());
+  }
+
+  @Test
+  void testConstructorWithoutCloud() {
+    HostMetadata meta = new HostMetadata("https://example.com/oidc", "acc-123", "ws-456");
+
+    assertEquals("https://example.com/oidc", meta.getOidcEndpoint());
+    assertEquals("acc-123", meta.getAccountId());
+    assertEquals("ws-456", meta.getWorkspaceId());
+    assertNull(meta.getCloud());
+  }
+}