Log number of deleted rows in prune_orphaned_activities

This gives feedback when to stop rerunning limited batches.

Most of the diff is just adjusting indentation; best reviewed
with whitespace-only changes hidden, e.g. `git diff -w`.

docs/docs/administration/CLI_tasks/database.md

@@ -59,6 +59,11 @@ This will prune activities which are no longer referenced by anything.
 Such activities might be the result of running `prune_objects` without `--prune-orphaned-activities`.
 The same notes and warnings apply as for `prune_objects`.
 
+The task will print out how many rows were freed in total in its last
+line of output in the form `Deleted 345 rows`.  
+When running the job in limited batches this can be used to determine
+when all orphaned activities have been deleted.
+
 === "OTP"
 
     ```sh

lib/mix/tasks/pleroma/database.ex

@@ -29,6 +29,7 @@ defmodule Mix.Tasks.Pleroma.Database do
       end
 
     # Prune activities who link to a single object
+    {:ok, %{:num_rows => del_single}} =
       """
       delete from public.activities
       where id in (
@@ -47,6 +48,7 @@ defmodule Mix.Tasks.Pleroma.Database do
       |> Repo.query([], timeout: :infinity)
 
     # Prune activities who link to an array of objects
+    {:ok, %{:num_rows => del_array}} =
       """
       delete from public.activities
       where id in (
@@ -63,6 +65,8 @@ defmodule Mix.Tasks.Pleroma.Database do
       )
       """
       |> Repo.query([], timeout: :infinity)
+
+    del_single + del_array
   end
 
   def run(["remove_embedded_objects" | args]) do
@@ -131,7 +135,9 @@ defmodule Mix.Tasks.Pleroma.Database do
 
     Logger.info(log_message)
 
-    prune_orphaned_activities(limit)
+    deleted = prune_orphaned_activities(limit)
+
+    Logger.info("Deleted #{deleted} rows")
   end
 
   def run(["prune_objects" | args]) do