サンプルデータで作ったスクリプト

<?php

$contents = [];

for ($i = 0; $i < 365; $i++) {
    $date = date('Y-m-d', strtotime("-{$i} day"));
    $data = [
        'app' => [
            "cpuAverage" => 9,
            "status" => 0,
        ],
        'console' => [
            "cpuAverage" => 9,
            "status" => 0,
        ],
        'rds' => [
            "cpuAverage" => 9,
            "status" => 0,
        ],
        'web' => [
            "cpuAverage" => 9,
            "status" => 0,
        ]
    ];
    $contents["histories"][$date] = $data;
}
$json = json_encode($contents);

file_put_contents("./status_sample_data.json", $json);