Output file silently ignores the delimiter passed

## Bug Report

**Describe the bug**
When using output file, it silently ignores the delimiter parameter.

Discussion started on Slack: https://fluent-all.slack.com/archives/C0CTQGHKJ/p1682626858152819

**To Reproduce**
- Steps to reproduce the problem:
Command:
```bash
./fluent-bit -i dummy -o file -p format=csv -p delimiter=';' -p file=my_file
```

```bash
cat my_file
1682626714.581559350,"dummy"
1682626715.581501656,"dummy"
```

It still uses the comma

**Expected behavior**
Either use the semicolon (or any other character passed, but semicolon should at least work for csv, no?) or throw an error

**Your Environment**
* Version used: 2.0.7
* Configuration: None
* Operating System and version: Ubuntu 22
* Filters and plugins: None

Start by running the provided fluent-bit command on Ubuntu 22 and inspect the file output plugin's CSV formatting and delimiter handling. Trace where the delimiter parameter is read and compare the generated file with the expected semicolon-separated output. Done means the delimiter is honored for CSV output, or an explicit error is returned for unsupported values.

Written by the indexing model from the issue text.