MM-51683 Re-add CODEOWNERS for Web Platform files (#22627)

CODEOWNERS

@@ -1 +1,9 @@
 /plugin/ @mattermost/toolkit
+
+/.github/workflows/channels-ci.yml @mattermost/web-platform
+/webapp/package.json @mattermost/web-platform
+/webapp/channels/package.json @mattermost/web-platform
+/webapp/Makefile @mattermost/web-platform
+/webapp/package-lock.json @mattermost/web-platform
+/webapp/platform/*/package.json @mattermost/web-platform
+/webapp/scripts @mattermost/web-platform

webapp/channels/CODEOWNERS

@@ -1,4 +0,0 @@
-# Web Platform should be assigned to review all PRs that involve changing dependencies in the app, either intentional or accidental.
-package.json @mattermost/web-platform
-*/package.json @mattermost/web-platform
-package-lock.json @mattermost/web-platform