Assorted scaffolder form help text improvements (#2467)

* Prompt the user for a description in templates

The text "Description of the component" was a little redundant since the
label already says "Description". This description text hints to the
user why they should bother adding an informative description.

* Inform user about lowercase, url-safe constraint

Create React App scaffolding fails when a name with spaces or other
non-url-safe chars are provided. Instead of making the user wait for a
failure, Backstage should tell them about this constraint up front.

plugins/scaffolder-backend/sample-templates/create-react-app/template.yaml

@@ -22,11 +22,11 @@ spec:
       component_id:
         title: Name
         type: string
-        description: Unique name of the component
+        description: Unique name of the component. Lowercase, URL-safe characters only.
       description:
         title: Description
         type: string
-        description: Description of the component
+        description: Help others understand what this website is for.
       use_typescript:
         title:  Use Typescript
         type: boolean

plugins/scaffolder-backend/sample-templates/docs-template/template.yaml

@@ -25,5 +25,5 @@ spec:
       description:
         title: Description
         type: string
-        description: Description of the component
+        description: Help others understand what these docs are about.
    

plugins/scaffolder-backend/sample-templates/react-ssr-template/template.yaml

@@ -24,4 +24,4 @@ spec:
       description:
         title: Description
         type: string
-        description: Description of the component
+        description: Help others understand what this website is for.

plugins/scaffolder-backend/sample-templates/springboot-grpc-template/template.yaml

@@ -25,7 +25,7 @@ spec:
       description:
         title: Description
         type: string
-        description: Description of the component
+        description: Help others understand what this service does.
       http_port:
         title: Port
         type: integer