Update MSF and Catalog ownership (#510)

## What changed?
<!-- Provide a bulleted list in the present tense -->
* In order to ensure that public documentation remains up-to-date with
development, the Catalog and Multi-Storefront teams want to have more
visibility over the updating process. This includes introducing code
ownership through the CODEOWNERS file, allowing for better visibility
and control over changes to documentation.

.github/CODEOWNERS

@@ -6,3 +6,12 @@
 # be identified in the format @org/team-name. Teams must have
 # explicit write access to the repository. In this example,
 # the octocats team in the octo-org organization owns all .md files.
+
+# @bigcommerce/team-catalog-ops
+reference/catalog @bigcommerce/team-catalog-ops
+archive/rest-catalog @bigcommerce/team-catalog-ops
+
+# @bigcommerce/team-multi-storefront
+docs/storefront/multi-storefront @bigcommerce/team-multi-storefront
+reference/channels.v3.yml @bigcommerce/team-multi-storefront
+reference/sites.v3.yml @bigcommerce/team-multi-storefront