[Feature Request] Trim CUSTOM_MODELS Variable

### 🥰 Feature Description

The `CUSTOM_MODELS` variable doesn't support spaces or newlines which makes it hard to manage large sets of custom models

### 🧐 Proposed Solution

Trim spaces and newlines from the `CUSTOM_MODELS` variable

### 📝 Additional Information

I'm currently handling spaces in `docker-compose` like this:
```yaml
environment:
OPENAI_API_KEY: ${OPENAI_API_KEY:-}
ANTHROPIC_API_KEY: ${ANTHROPIC_API_KEY:-}
CUSTOM_MODELS: >
-all,
gpt-4.1@OpenAI,
chatgpt-4o-latest@OpenAI,
gpt-4o@OpenAI,
gpt-4o-mini@OpenAI,
o1-pro@OpenAI,
o3@OpenAI,
o3-mini@OpenAI,
o4-mini@OpenAI,
gpt-4.1-mini@OpenAI,
gpt-4.1-nano@OpenAI,
claude-3-7-sonnet-latest@Anthropic,
claude-3-5-haiku-latest@Anthropic,
claude-3-opus-latest@Anthropic
command:
- sh
- -c
- export CUSTOM_MODELS=$(echo "$$CUSTOM_MODELS" | tr -d " ") && node server.js
```