Add counter filter (#3921) (#3945)

* Add counter filter

* move counter filter doc to existing chapter

* Use existing typerror exception from Counter

* Match counter filter example task name and output

(cherry picked from commit 9642a15d34)

Co-authored-by: Rémy Keil <remy.keil@gmail.com>

changelogs/fragments/3921-add-counter-filter-plugin.yml

@@ -0,0 +1,4 @@
+---
+add plugin.filter:
+  - name: counter
+    description: Counts hashable elements in a sequence