[5.x] Allow custom nocache db connection

[macaws]

The Problem

Users cannot specify a separate database connection for the nocache_regions table without modifying Statamic core code. Sometimes, this table can get really big and you may not want to include it on frequent backups. You may also want to move this table specifically closer to the Statamic install to reduce latency.

The Solution

This PR adds a configuration option to allow specifying a different database connection for the nocache_regions table.

Backward Compatibility

This change is fully backward compatible as it defaults to the current behavior (using the default database connection) when no configuration is provided.

Usage Example

// In .env file
STATAMIC_NOCACHE_DB_CONNECTION=nocache

// Or in config/statamic/static_caching.php
'nocache_db_connection' => 'nocache',

// In config/database.php
        'nocache' => [
            'driver' => 'mysql',
            'host' => env('NOCACHE_DB_HOST', env('DB_HOST', '127.0.0.1')),
            'port' => env('NOCACHE_DB_PORT', env('DB_PORT', '3306')),
            'database' => env('NOCACHE_DB_DATABASE', 'nocache'),
            'username' => env('NOCACHE_DB_USERNAME', env('DB_USERNAME')),
            'password' => env('NOCACHE_DB_PASSWORD', env('DB_PASSWORD')),
            'charset' => 'utf8mb4',
            'collation' => 'utf8mb4_unicode_ci',
            'prefix' => '',
            'strict' => true,
            'engine' => null,
        ],