Capture DatabricksError when retrying API calls (#427)

## What changes are proposed in this pull request?

When requests are retried, there is currently no information available
to the caller to understand why. On retries no exception is logged and
on final retry, the cause is only available if an `IOException` were the
original source of failure rather. `DatabricksError` feels like a more
useful error to surface as this will capture the error from the server
which would have evaluated into a retriable error.

Currently the stacktrace appears as follows, which doesn't provide much
information:
```
com.databricks.sdk.core.DatabricksException: Request GET /api/2.1/unity-catalog/tables?catalog_name=<REDACTED>&schema_name=<REDACTED> failed after 4 retries
\tat com.databricks.sdk.core.ApiClient.executeInner(ApiClient.java:282)
\tat com.databricks.sdk.core.ApiClient.getResponse(ApiClient.java:235)
\tat com.databricks.sdk.core.ApiClient.execute(ApiClient.java:227)
\tat com.databricks.sdk.core.ApiClient.GET(ApiClient.java:148)
\tat com.databricks.sdk.service.catalog.TablesImpl.list(TablesImpl.java:47)
\tat com.databricks.sdk.support.Paginator.flipNextPage(Paginator.java:58)
\tat com.databricks.sdk.support.Paginator.<init>(Paginator.java:51)
\tat com.databricks.sdk.service.catalog.TablesAPI.list(TablesAPI.java:102)
\tat com.databricks.sdk.service.catalog.TablesAPI.list(TablesAPI.java:89)
```

## How is this tested?

Unit tests added.

Signed-off-by: Thomas Powell <tpowell@palantir.com>
Co-authored-by: Thomas Powell <tpowell@palantir.com>
Co-authored-by: Renaud Hartert <renaud.hartert@databricks.com>

Author: 3 people

NEXT_CHANGELOG.md

@@ -9,5 +9,6 @@
 ### Documentation
 
 ### Internal Changes
+* Capture DatabricksError when retrying API calls ([#427](https://github.com/databricks/databricks-sdk-java/pull/427)).
 
 ### API Changes

databricks-sdk-java/src/main/java/com/databricks/sdk/core/ApiClient.java

@@ -247,12 +247,13 @@ private Response executeInner(Request in, String path) {
       }
       if (attemptNumber == maxAttempts) {
         throw new DatabricksException(
-            String.format("Request %s failed after %d retries", in, maxAttempts), err);
+            String.format("Request %s failed after %d retries", in, maxAttempts), databricksError);
       }
 
       // Retry after a backoff.
       long sleepMillis = getBackoffMillis(out, attemptNumber);
-      LOG.debug(String.format("Retry %s in %dms", in.getRequestLine(), sleepMillis));
+      LOG.debug(
+          String.format("Retry %s in %dms", in.getRequestLine(), sleepMillis), databricksError);
       try {
         timer.sleep(sleepMillis);
       } catch (InterruptedException ex) {

databricks-sdk-java/src/test/java/com/databricks/sdk/core/ApiClientTest.java

@@ -11,6 +11,7 @@
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import java.io.IOException;
 import java.net.MalformedURLException;
 import java.net.URL;
@@ -88,12 +89,14 @@ private <T> void runApiClientTest(
     runApiClientTest(client, request, clazz, expectedResponse);
   }
 
-  private void runFailingApiClientTest(
+  @CanIgnoreReturnValue
+  private DatabricksException runFailingApiClientTest(
       Request request, List<ResponseProvider> responses, Class<?> clazz, String expectedMessage)
       throws IOException {
     DatabricksException exception =
         runFailingApiClientTest(request, responses, clazz, DatabricksException.class);
     assertEquals(exception.getMessage(), expectedMessage);
+    return exception;
   }
 
   private <T extends Throwable> T runFailingApiClientTest(
@@ -217,16 +220,21 @@ void retry429() throws IOException {
   @Test
   void failAfterTooManyRetries() throws IOException {
     Request req = getBasicRequest();
-    runFailingApiClientTest(
-        req,
-        Arrays.asList(
-            getTooManyRequestsResponseWithRetryAfterDateHeader(req),
-            getTooManyRequestsResponse(req),
-            getTooManyRequestsResponse(req),
-            getTooManyRequestsResponse(req),
-            getSuccessResponse(req)),
-        MyEndpointResponse.class,
-        "Request GET /api/my/endpoint failed after 4 retries");
+    DatabricksException exception =
+        runFailingApiClientTest(
+            req,
+            Arrays.asList(
+                getTooManyRequestsResponseWithRetryAfterDateHeader(req),
+                getTooManyRequestsResponse(req),
+                getTooManyRequestsResponse(req),
+                getTooManyRequestsResponse(req),
+                getSuccessResponse(req)),
+            MyEndpointResponse.class,
+            "Request GET /api/my/endpoint failed after 4 retries");
+    assertInstanceOf(DatabricksError.class, exception.getCause());
+    DatabricksError cause = (DatabricksError) exception.getCause();
+    assertEquals(cause.getErrorCode(), "TOO_MANY_REQUESTS");
+    assertEquals(cause.getStatusCode(), 429);
   }
 
   @Test