Configuring using "manimgl --config" breaks the config file.

### Describe the error
Hi there,
I ran `manimgl --config` to modify **global** config and manim seems to have corrupted my `default_config.yml`. The new file is missing the `file_writer_config`, causing video generation errors. I've attached the before and after files( I have to use .txt to meet github's restriction).
[default_config-after.yml.txt](https://github.com/user-attachments/files/17456962/default_config-after.yml.txt)
[default_config-before.yml.txt](https://github.com/user-attachments/files/17456963/default_config-before.yml.txt)

### Code and Error
**Code**:
`manimgl --config`
`manimgl main.py main -w --finder --prerun --show_animation_progress`

**Error**:
```bash
Traceback (most recent call last):
File "/Library/Frameworks/Python.framework/Versions/3.12/bin/manimgl", line 8, in
sys.exit(main())
^^^^^^
File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/manimlib/__main__.py", line 21, in main
config = manimlib.config.get_configuration(args)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/manimlib/config.py", line 509, in get_configuration
"file_writer_config": get_file_writer_config(args, custom_config),
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/manimlib/config.py", line 415, in get_file_writer_config
**custom_config["file_writer_config"],
~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^
KeyError: 'file_writer_config'

```

### Environment
**OS System**: MacOS 13
**manim version**: master 1.7.0
**python version**: 3.12.6