Add end-to-end test for creating a group issue board via the GUI

What does this MR do?

This MR covers one of the two scenarios described in this issue gitlab-org/quality/testcases#226 (closed)#.

Besides creating the new test, this MR also creates an issue board component that can be used by both groups and projects since they share the same elements and methods.

Finally, an existing test is updated to remove an expectation that doesn't make sense anymore due to a feature change that was causing the test to fail (!17937 (merged)).

More details in the commit messages.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

app/assets/javascripts/boards/components/boards_selector.vue

@@ -305,7 +305,11 @@ export default {
         <div v-if="canAdminBoard">
           <gl-dropdown-divider />
 
-          <gl-dropdown-item v-if="multipleIssueBoardsAvailable" @click.prevent="showPage('new')">
+          <gl-dropdown-item
+            v-if="multipleIssueBoardsAvailable"
+            data-qa-selector="create_new_board_button"
+            @click.prevent="showPage('new')"
+          >
             {{ s__('IssueBoards|Create new board') }}
           </gl-dropdown-item>