[MM-62409] Generate and publish code coverage for webapp (#31144)

* Generate and publish code coverage for webapp

* Upate coverage output path

* Simplify coverage patterns

* Disable coverage file search

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Co-authored-by: Mattermost Build <build@mattermost.com>

.github/codecov.yml

@@ -9,5 +9,8 @@ coverage:
     project:
       default:
         threshold: 1.0
+codecov:
+  notify:
+    after_n_builds: 2 # Server and webapp at this point
 ignore:
   - ^store/storetest.*