Increase number of simultaneous connections per Workspace (#548)

## What changes are proposed in this pull request?
Increase number of simultaneous connections per Workspace from 2 to 20.
This allows for better parallelization for customers. The new default
matches the Databricks Python SDK default configuration.

## How is this tested?
N/A

Author: hectorcast-db

NEXT_CHANGELOG.md

@@ -3,6 +3,7 @@
 ## Release v0.70.0
 
 ### New Features and Improvements
+* Increase maximum number of concurrent HTTP connections per Workspace from 2 to 20.
 
 ### Bug Fixes
 

databricks-sdk-java/src/main/java/com/databricks/sdk/core/commons/CommonsHttpClient.java

@@ -141,7 +141,11 @@ private CommonsHttpClient(Builder builder) {
     } else {
       PoolingHttpClientConnectionManager connectionManager =
           new PoolingHttpClientConnectionManager();
+      // Total number of connections allowed by the connection manager.
       connectionManager.setMaxTotal(100);
+      // Maximum number of connections per route. In most cases, this means per Workspace.
+      // DataPlane resources have a dedicated route and are not subject to this limit.
+      connectionManager.setDefaultMaxPerRoute(20);
       httpClientBuilder.setConnectionManager(connectionManager);
     }
     if (builder.requestRetryHandler != null) {