message: Fix example plugin link in catalog config doc
  A link to the example artist-lookup-component.yaml file was broken due to a
  change in repo directory structure. This commit updates the broken link to
  reflect the new location.
diff: @@ -23,7 +23,7 @@ Locations are added to the catalog under the `catalog.locations` key:
  catalog:
  locations:
  - type: url
  - target: https://github.com/backstage/backstage/blob/master/packages/catalog-model/examples/artist-lookup-component.yaml
  + target: https://github.com/backstage/backstage/blob/master/packages/catalog-model/examples/components/artist-lookup-component.yaml
  ```
  The `url` type locations are handled by a standard processor included with the
  