feat: add archived application text field to EinundzwanzigPleb model

This commit introduces a new field `archived_application_text` to the EinundzwanzigPleb model. The application text of a Pleb is now archived before the association status is updated and the application text is set to null. A migration file is also added to update the database schema.

database/migrations/2024_09_30_171153_add_copy_field_application_text_to_einundzwanzig_plebs_table.php

@@ -0,0 +1,27 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration {
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::table('einundzwanzig_plebs', function (Blueprint $table) {
+            $table->text('archived_application_text')->nullable()->after('application_text');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('einundzwanzig_plebs', function (Blueprint $table) {
+            //
+        });
+    }
+};