Added Catalog Collator filter example

Signed-off-by: Andre Wanlin <awanlin@spotify.com>

docs/features/search/collators.md

@@ -35,6 +35,10 @@ backend.start();
 
 ### Configuring the Catalog Collator
 
+The following sections outlines the available configurations for this collator.
+
+#### Scheduling
+
 The default schedule for the Catalog Collator is to run every 10 minutes, you can provide your own schedule by adding it to your config:
 
 ```yaml title="app-config.yaml
@@ -50,6 +54,42 @@ search:
         timeout: { minutes: 3 }
 ```
 
+#### Filtering
+
+You may wish to collate specific subsets of entities in your Catalog, this can be accomplished using the `filter` configuration option. Here's a basic example:
+
+```yaml title"app-config.yaml"
+search:
+  collators:
+    catalog:
+      filter:
+        kind: ['component', 'api']
+        spec.lifecycle: production
+```
+
+The above example will only collate entities that are `kind` equal to `component` or `api` AND have a `spec.lifecycle` set to `production`
+
+You can also apply a more advanced filter like this:
+
+```yaml title"app-config.yaml"
+search:
+  collators:
+    catalog:
+      filter:
+        - kind: ['API']
+          spec.type: openapi
+        - kind: ['Component']
+          spec.lifecycle: experimental
+```
+
+Now with this example it will collate all entities that are `kind` equal to `api` with a `spec.type` equal to `openapi` OR all entities that are `kind` equal to `component` AND have a `spec.lifecycle` set to `experimental`
+
+:::tip
+
+The filter configuration is implemented using the `EntityFilterQuery` syntax. The [reference documentation on `EntityFilterQuery`](https://backstage.io/docs/reference/catalog-client.entityfilterquery/) provides more details.
+
+:::
+
 ## TechDocs
 
 The TechDocs collator will index all the TechDocs in your Catalog. It is installed by default but if you need to add it manually here's how.