Rename postcss.config.js to postcss.config.cjs

On Default Laravel Sail Install the original STUB causes an error this solves the issue.

Renaming postcss.config.cjs to postcss.config.js as the error outlines fixes the issue.

Fixes Error:
````
node:internal/process/promises:288
            triggerUncaughtException(err, true /* fromPromise */);
            ^

[Failed to load PostCSS config: Failed to load PostCSS config (searchPath: /var/www/html): [Failed to load PostCSS config] Failed to load PostCSS config (searchPath: /var/www/html): [ReferenceError] module is not defined in ES module scope
This file is being treated as an ES module because it has a '.js' file extension and '/var/www/html/package.json' contains "type": "module". To treat it as a CommonJS script, rename it to use the '.cjs' file extension.
ReferenceError: module is not defined in ES module scope
This file is being treated as an ES module because it has a '.js' file extension and '/var/www/html/package.json' contains "type": "module". To treat it as a CommonJS script, rename it to use the '.cjs' file extension.
    at file:///var/www/html/postcss.config.js:1:1
    at ModuleJob.run (node:internal/modules/esm/module_job:194:25)
]

Node.js v18.16.0
````

Author: ahosker