correct the doc of backend trace sampling with the latest configuration (#6085)

CHANGES.md

@@ -59,6 +59,7 @@ Release Notes.
 * Update the documents of backend fetcher and self observability about the latest configurations.
 * Add documents about the group name of service.
 * Update docs about the latest UI.
+* Update the document of backend trace sampling with the latest configuration.
 
 All issues and pull requests are [here](https://github.com/apache/skywalking/milestone/68?closed=1)
 

docs/en/setup/backend/trace-sampling.md

@@ -14,7 +14,7 @@ In **agent-analyzer** module, you will find `sampleRate` setting.
 agent-analyzer:
   default:
     ...
-    sampleRate: ${SW_TRACE_SAMPLE_RATE:1000} # The sample rate precision is 1/10000. 10000 means 100% sample in default.
+    sampleRate: ${SW_TRACE_SAMPLE_RATE:10000} # The sample rate precision is 1/10000. 10000 means 100% sample in default.
     forceSampleErrorSegment: ${SW_FORCE_SAMPLE_ERROR_SEGMENT:true} # When sampling mechanism activated, this config would make the error status segment sampled, ignoring the sampling rate.
     slowTraceSegmentThreshold: ${SW_SLOW_TRACE_SEGMENT_THRESHOLD:-1} # Setting this threshold about the latency would make the slow trace segments sampled if they cost more time, even the sampling mechanism activated. The default value is `-1`, which means would not sample slow traces. Unit, millisecond.
 ```