create-app: add EntityLinksCard to the System EntityPage

Signed-off-by: Jason Nguyen <jsn.dev@outlook.com>

.changeset/young-trees-rescue.md

@@ -0,0 +1,24 @@
+---
+'@backstage/create-app': patch
+---
+
+Added `EntityLinksCard` to the system `EntityPage`.
+
+For an existing installation where you want to display the links card for entity pages of kind `system` you should make the following adjustment to `packages/app/src/components/catalog/EntityPage.tsx`
+
+```diff
+const systemPage = (
+  ...
+        <Grid item md={6} xs={12}>
+          <EntityCatalogGraphCard variant="gridItem" height={400} />
+        </Grid>
++       <Grid item md={4} xs={12}>
++         <EntityLinksCard />
++       </Grid>
+-      <Grid item md={6}>
++      <Grid item md={8}>
+          <EntityHasComponentsCard variant="gridItem" />
+        </Grid>
+  ...
+);
+```

packages/create-app/templates/default-app/packages/app/src/components/catalog/EntityPage.tsx

@@ -324,7 +324,10 @@ const systemPage = (
         <Grid item md={6} xs={12}>
           <EntityCatalogGraphCard variant="gridItem" height={400} />
         </Grid>
-        <Grid item md={6}>
+        <Grid item md={4} xs={12}>
+          <EntityLinksCard />
+        </Grid>
+        <Grid item md={8}>
           <EntityHasComponentsCard variant="gridItem" />
         </Grid>
         <Grid item md={6}>