[MINOR] improvement(server): LOG the exception call stack while unregisterShuffle (#2228)

### What changes were proposed in this pull request?

LOG the exception call stack while unregisterShuffle

### Why are the changes needed?

Easy to find the error call stack.

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?

No need.

Author: maobaolong

server/src/main/java/org/apache/uniffle/server/ShuffleServerGrpcService.java

@@ -172,6 +172,7 @@ public void unregisterShuffleByAppId(
         }
       } catch (Exception e) {
         status = StatusCode.INTERNAL_ERROR;
+        LOG.error("App {} exception while unregisterShuffleByAppId", appId, e);
       }
 
       auditContext.withStatusCode(status);
@@ -215,6 +216,7 @@ public void unregisterShuffle(
         }
       } catch (Exception e) {
         status = StatusCode.INTERNAL_ERROR;
+        LOG.error("App {} exception while unregisterShuffle", appId, e);
       }
 
       auditContext.withStatusCode(status);