Add @XSAM as project approver

[Requirements](https://github.com/open-telemetry/community/blob/master/community-membership.md#requirements-2)
- [X] >=10 substantive contributions (open-telemetry/opentelemetry-go-contrib#134, open-telemetry/opentelemetry-go-contrib#153, open-telemetry/opentelemetry-go-contrib#221, open-telemetry/opentelemetry-go-contrib#298, open-telemetry/opentelemetry-go-contrib#303, open-telemetry#796, open-telemetry#905, open-telemetry#986, open-telemetry#1044, open-telemetry#1031, open-telemetry#1102)
- [X] Active >1mo
- [X] add to CODEOWNERS  (done in this pull)
- [X] Add to CONTRIBUTING.md (done in this pull)
- [X] Maintainer nomination: @MrAlias
- [ ] Other maintainer(s) (@Aneurysm9) sign-off
- [ ]  Add to @open-telemetry/go-approvers

CODEOWNERS

@@ -6,12 +6,12 @@
 #
 # Learn about membership in OpenTelemetry community:
 #  https://github.com/open-telemetry/community/blob/master/community-membership.md
-# 
 #
-# Learn about CODEOWNERS file format: 
+#
+# Learn about CODEOWNERS file format:
 #  https://help.github.com/en/articles/about-code-owners
 #
 
-* @jmacd @lizthegrey @MrAlias @Aneurysm9 @evantorrie
+* @jmacd @lizthegrey @MrAlias @Aneurysm9 @evantorrie @XSAM
 
 CODEOWNERS @MrAlias @Aneurysm9

CONTRIBUTING.md

@@ -349,6 +349,7 @@ Approvers:
 - [Liz Fong-Jones](https://github.com/lizthegrey), Honeycomb
 - [Evan Torrie](https://github.com/evantorrie), Verizon Media
 - [Josh MacDonald](https://github.com/jmacd), LightStep
+- [Sam Xie](https://github.com/XSAM)
 
 Maintainers: