feat(cli): support multiple env file argument (#26527)
Closes #26425
## Overview
This PR adds support for specifying multiple environment files as
arguments when using the Deno CLI. Subsequent files override
pre-existing variables defined in previous files.
If the same variable is defined in the environment and in the file, the
value from the environment takes precedence.
## Example Usage
```bash
deno run --allow-env --env-file --env-file=".env.one" --env-file=".env.two" script.ts
```
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Co-authored-by: Bartek Iwańczuk <biwanczuk@gmail.com>
