Added .banprune command which sets how many days worth of messages will be pruned when bot (soft)bans a person either through a command or another punishment feature. Also updated .next usage string.

src/NadekoBot/Migrations/Postgresql/20220831142735_banprune.cs

@@ -0,0 +1,25 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace NadekoBot.Migrations.PostgreSql
+{
+    public partial class banprune : Migration
+    {
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<int>(
+                name: "prunedays",
+                table: "bantemplates",
+                type: "integer",
+                nullable: true);
+        }
+
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropColumn(
+                name: "prunedays",
+                table: "bantemplates");
+        }
+    }
+}