chore: add @CycloneDX/core-team as default reviewers (#298)

Signed-off-by: Jan Kowalleck <jan.kowalleck@gmail.com>

Author: jkowalleck

CODEOWNERS

@@ -0,0 +1,5 @@
+# see https://docs.github.com/en/github/creating-cloning-and-archiving-repositories/about-code-owners
+
+# all Core Team members are default-reviewers of new pull requests.
+# see https://github.com/orgs/CycloneDX/teams/core-team
+*  @CycloneDX/core-team