zpages: Add @dashpole as codeowner (#4170)

Co-authored-by: Chester Cheung <cheung.zhy.csu@gmail.com>

Author: pellared

CODEOWNERS

@@ -58,5 +58,5 @@ samplers/aws/xray/                                                      @open-te
 samplers/jaegerremote/                                                  @open-telemetry/go-approvers
 samplers/probability/consistent/                                        @open-telemetry/go-approvers @MadVikingGod
 
-zpages/                                                                 @open-telemetry/go-approvers
+zpages/                                                                 @open-telemetry/go-approvers @dashpole
 instrgen/                                                               @open-telemetry/go-approvers @open-telemetry/go-instrumentation-approvers @MrAlias @pdelewski