catalog: make the external createComponent route optional, hiding the button if it is not set

plugins/catalog/src/components/CatalogPage/CatalogPage.tsx

@@ -167,14 +167,16 @@ const CatalogPageContents = () => {
       />
       <Content>
         <ContentHeader title={selectedTab ?? ''}>
-          <Button
-            component={RouterLink}
-            variant="contained"
-            color="primary"
-            to={createComponentLink()}
-          >
-            Create Component
-          </Button>
+          {createComponentLink && (
+            <Button
+              component={RouterLink}
+              variant="contained"
+              color="primary"
+              to={createComponentLink()}
+            >
+              Create Component
+            </Button>
+          )}
           {showAddExampleEntities && (
             <Button
               className={styles.buttonSpacing}

plugins/catalog/src/routes.ts

@@ -18,4 +18,5 @@ import { createExternalRouteRef } from '@backstage/core';
 
 export const createComponentRouteRef = createExternalRouteRef({
   id: 'create-component',
+  optional: true,
 });