Modernize generated .gitignore to cover environment-specific dotenv files

## Description

The `.gitignore` generated by `express-generator --git` currently ignores `.env`, but does not ignore environment-specific dotenv files such as `.env.local`, `.env.development`, or `.env.production`.

For example, the current template contains:

```gitignore
# dotenv environment variables file
.env
```

I propose updating this to:

```gitignore
# dotenv environment variable files
.env
.env.*
!.env.example
```

This would help protect environment-specific configuration files that may contain credentials or other sensitive values, while still allowing projects to commit a safe `.env.example` file.

## Why?

Node.js applications commonly use multiple dotenv files for different environments, for example:

* `.env`
* `.env.local`
* `.env.development`
* `.env.production`
* `.env.test`

Ignoring only `.env` does not cover these additional `.env.*` files.

The proposed pattern follows a commonly used approach in modern Node.js project templates.

## Proposed change

Update the JavaScript `.gitignore` template in:

`templates/js/gitignore`

from:

```gitignore
# dotenv environment variables file
.env
```

to:

```gitignore
# dotenv environment variable files
.env
.env.*
!.env.example
```

I would also be happy to add or update the relevant tests if this change is accepted.

Would this be a change the maintainers would be open to?