🔧 chore(base.py, constants.py, llms.py): add info field to TemplateField and OPENAI_API_BASE_INFO constant

The `info` field is added to the `TemplateField` class to provide additional information about the field. The `OPENAI_API_BASE_INFO` constant is added to the `constants.py` file to provide information about the base URL of the OpenAI API and how it can be changed to use other APIs like Prem and LocalAI. The `info` field is set to `OPENAI_API_BASE_INFO` for the `openai_api_base` field in the `LLMFrontendNode` class in `llms.py`.