Add Markdown support in the About Card description section

To keep consistency with the Scaffolder template cards this commit
introduces Markdown support in the Catalog components About Card

Signed-off-by: Konstantin Matyukhin <kmatyukhin@gmail.com>

packages/catalog-model/examples/components/petstore-component.yaml

@@ -2,8 +2,11 @@ apiVersion: backstage.io/v1alpha1
 kind: Component
 metadata:
   name: petstore
-  # This is an extra long description
-  description: The Petstore is an example API used to show features of the OpenAPI spec.
+  # This is an extra long description with Markdown
+  description: |
+    [The Petstore](http://petstore.example.com) is an example API used to show features of the OpenAPI spec.
+    - First item
+    - Second item
   links:
     - url: https://github.com/swagger-api/swagger-petstore
       title: GitHub Repo