Add .env property to allow to set more Browser flags

I used the tool locally and I missed the following feature to set a custom browser path:

```js
const createReports = async (endpoint, headers, events, urls, audit) => {
const additionalBrowserFlags = {};
if (process.env.BROWSER_PATH)
additionalBrowserFlags['chromePath'] = process.env.BROWSER_PATH;

const browser = await chromeLauncher.launch({
chromeFlags: ['--headless'],
...additionalBrowserFlags,
});
...
}
```

.env file:

```text
...
BROWSER_PATH=C:\\Program Files (x86)\\Microsoft\\Edge\\Application\\msedge.exe
...
```

A such configuration would allow to test with multiple Chromium based browser like in my case Edge.
What do you think? Would that be a proper enhancement?