REST: Add property for configuring user agent in http client (#13234)

Co-authored-by: Prashant Singh <prashant.singh@snowflake.com>

Author: singhpk234

core/src/main/java/org/apache/iceberg/rest/HTTPClient.java

@@ -86,6 +86,7 @@ public class HTTPClient extends BaseHTTPClient {
   static final String REST_PROXY_PORT = "rest.client.proxy.port";
   static final String REST_PROXY_USERNAME = "rest.client.proxy.username";
   static final String REST_PROXY_PASSWORD = "rest.client.proxy.password";
+  static final String REST_USER_AGENT = "rest.client.user-agent";
 
   @VisibleForTesting
   static final String REST_CONNECTION_TIMEOUT_MS = "rest.client.connection-timeout-ms";
@@ -122,6 +123,11 @@ private HTTPClient(
     int maxRetries = PropertyUtil.propertyAsInt(properties, REST_MAX_RETRIES, 5);
     clientBuilder.setRetryStrategy(new ExponentialHttpRequestRetryStrategy(maxRetries));
 
+    String userAgent = PropertyUtil.propertyAsString(properties, REST_USER_AGENT, null);
+    if (userAgent != null) {
+      clientBuilder.setUserAgent(userAgent);
+    }
+
     if (proxy != null) {
       if (proxyCredsProvider != null) {
         clientBuilder.setDefaultCredentialsProvider(proxyCredsProvider);

core/src/test/java/org/apache/iceberg/rest/TestHTTPClient.java

@@ -72,6 +72,8 @@ public class TestHTTPClient {
 
   private static final int PORT = 1080;
   private static final String BEARER_AUTH_TOKEN = "auth_token";
+  private static final String USER_AGENT = "User-Agent";
+  private static final String TEST_USER_AGENT = "Test-User-Agent";
   private static final String URI = String.format("http://127.0.0.1:%d", PORT);
   private static final ObjectMapper MAPPER = RESTObjectMapper.mapper();
 
@@ -96,7 +98,10 @@ public static class TLSConfigurerMissingNoArgCtor implements TLSConfigurer {
   public static void beforeClass() {
     mockServer = startClientAndServer(PORT);
     restClient =
-        HTTPClient.builder(ImmutableMap.of()).uri(URI).withAuthSession(AuthSession.EMPTY).build();
+        HTTPClient.builder(ImmutableMap.of(HTTPClient.REST_USER_AGENT, TEST_USER_AGENT))
+            .uri(URI)
+            .withAuthSession(AuthSession.EMPTY)
+            .build();
     icebergBuildGitCommitShort = IcebergBuild.gitCommitShortId();
     icebergBuildFullVersion = IcebergBuild.fullVersion();
   }
@@ -516,7 +521,8 @@ private static String addRequestTestCaseAndGetPath(HttpMethod method, Item body,
             .withMethod(method.name().toUpperCase(Locale.ROOT))
             .withHeader("Authorization", "Bearer " + BEARER_AUTH_TOKEN)
             .withHeader(HTTPClient.CLIENT_VERSION_HEADER, icebergBuildFullVersion)
-            .withHeader(HTTPClient.CLIENT_GIT_COMMIT_SHORT_HEADER, icebergBuildGitCommitShort);
+            .withHeader(HTTPClient.CLIENT_GIT_COMMIT_SHORT_HEADER, icebergBuildGitCommitShort)
+            .withHeader(USER_AGENT, TEST_USER_AGENT);
 
     if (method.usesRequestBody()) {
       mockRequest = mockRequest.withBody(asJson);