fix: remove default value and restore agent.config entry for propagation_exclude_ports

- Change PROPAGATION_EXCLUDE_PORTS default from "8123" to "" (no ports excluded by default)
- Add config entry back to agent.config with empty default so env var SW_PLUGIN_HTTPCLIENT_PROPAGATION_EXCLUDE_PORTS works correctly
- E2E clickhouse test sets the env var to "8123" explicitly

Author: daguimu

apm-sniffer/apm-sdk-plugin/httpclient-commons/src/main/java/org/apache/skywalking/apm/plugin/httpclient/HttpClientPluginConfig.java

@@ -40,12 +40,10 @@ public static class HttpClient {
              * and from injecting the {@code sw8} tracing headers into those outbound
              * requests.
              *
-             * <p>Default: {@code "8123"} (ClickHouse HTTP interface).
-             *
-             * <p>Example – also exclude port 9200 (Elasticsearch):
+             * <p>Example – exclude ClickHouse and Elasticsearch ports:
              * {@code plugin.httpclient.propagation_exclude_ports=8123,9200}
              */
-            public static String PROPAGATION_EXCLUDE_PORTS = "8123";
+            public static String PROPAGATION_EXCLUDE_PORTS = "";
         }
 
         @PluginConfig(root = HttpClientPluginConfig.class)

apm-sniffer/config/agent.config

@@ -220,6 +220,8 @@ plugin.tomcat.collect_http_params=${SW_PLUGIN_TOMCAT_COLLECT_HTTP_PARAMS:false}
 plugin.springmvc.collect_http_params=${SW_PLUGIN_SPRINGMVC_COLLECT_HTTP_PARAMS:false}
 #  This config item controls that whether the HttpClient plugin should collect the parameters of the request
 plugin.httpclient.collect_http_params=${SW_PLUGIN_HTTPCLIENT_COLLECT_HTTP_PARAMS:false}
+#  Comma-separated list of destination ports whose outbound HTTP requests will be completely skipped by the httpclient-4.x interceptor (no exit span created, no sw8 headers injected).
+plugin.httpclient.propagation_exclude_ports=${SW_PLUGIN_HTTPCLIENT_PROPAGATION_EXCLUDE_PORTS:}
 #  When `COLLECT_HTTP_PARAMS` is enabled, how many characters to keep and send to the OAP backend, use negative values to keep and send the complete parameters, NB. this config item is added for the sake of performance.  
 plugin.http.http_params_length_threshold=${SW_PLUGIN_HTTP_HTTP_PARAMS_LENGTH_THRESHOLD:1024}
 #  When `include_http_headers` declares header names, this threshold controls the length limitation of all header values. use negative values to keep and send the complete headers. Note. this config item is added for the sake of performance.