Update CODEOWNERS (#880)

Align with
https://github.com/aws-observability/aws-otel-python-instrumentation/blob/main/.github/CODEOWNERS

*Issue #, if available:*

*Description of changes:*


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under the terms of the Apache 2.0 license.

.github/CODEOWNERS

@@ -1,3 +1,5 @@
-# https://help.github.com/articles/about-codeowners/
+# Learn about CODEOWNERS file format:
+#  https://help.github.com/en/articles/about-code-owners
 
-* @aws-observability/adot-sdk-maintainers
+# Default owners for the entire repo
+* @aws-observability/aws-application-signals-maintainers