fix: use repo metadata to populate nodejs CODEOWNERS (#936)

* fix: use repo metadata to populate nodejs CODEOWNERS

* chore: small formatting tweaks

Co-authored-by: Benjamin Coe <bencoe@google.com>

synthtool/gcp/templates/node_library/.github/CODEOWNERS

@@ -0,0 +1,13 @@
+# Code owners file.
+# This file controls who is tagged for review for any given pull request.
+#
+# For syntax help see:
+# https://help.github.com/en/github/creating-cloning-and-archiving-repositories/about-code-owners#codeowners-syntax
+
+
+# The yoshi-nodejs team is the default owner for nodejs repositories.
+{%- if 'codeowner_team' in metadata['repo'] %}
+*     @googleapis/yoshi-nodejs {{ metadata['repo']['codeowner_team'] }}
+{%- else %}
+*     @googleapis/yoshi-nodejs
+{%- endif %}