Add @XSAM and @dmathieu as repository maintainers (#5838)

Copy of open-telemetry/opentelemetry-go#5558

Co-authored-by: Sam Xie <sam@samxie.me>

CODEOWNERS

@@ -23,7 +23,7 @@
 
 * @open-telemetry/go-approvers
 
-CODEOWNERS @MrAlias @MadVikingGod @pellared @dashpole
+CODEOWNERS @MrAlias @MadVikingGod @pellared @dashpole @XSAM @dmathieu
 
 bridges/otelslog                                                        @open-telemetry/go-approvers @MrAlias @pellared
 bridges/otellogrus/                                                     @open-telemetry/go-approvers @dmathieu @pellared

CONTRIBUTING.md

@@ -125,15 +125,15 @@ See the [public meeting notes](https://docs.google.com/document/d/1E5e7Ld0NuU1iV
 
 Approvers:
 
-- [Sam Xie](https://github.com/XSAM), Cisco/AppDynamics
 - [Chester Cheung](https://github.com/hanyuancheung), Tencent
-- [Damien Mathieu](https://github.com/dmathieu), Elastic
 
 Maintainers:
 
-- [David Ashpole](https://github.com/dashpole), Google
 - [Aaron Clawson](https://github.com/MadVikingGod), LightStep
+- [Damien Mathieu](https://github.com/dmathieu), Elastic
+- [David Ashpole](https://github.com/dashpole), Google
 - [Robert Pająk](https://github.com/pellared), Splunk
+- [Sam Xie](https://github.com/XSAM), Cisco/AppDynamics
 - [Tyler Yahn](https://github.com/MrAlias), Splunk
 
 Emeritus: