`api_key_cmd` won't work if command argument contain spaces

I get `Config api_key_cmd did not return a value when executed` when using the following config:
```
require("chatgpt").setup({
api_key_cmd = "/usr/bin/secret-tool lookup Path 'OpenAI API Key - chatGPT.nvim'"
})
```

But looking up a key that doesn't contain spaces works:
```
require("chatgpt").setup({
api_key_cmd = "/usr/bin/secret-tool lookup Uuid 112c0e39f57244d4b25fed63c68b7c65"
})
```

Please note the 2 commands above lookup the same entry and both work on the terminal. Therefore, parsing `api_key_cmd` does not work when arguments contain spaces, such as `'OpenAI API Key - chatGPT.nvim'`. The problem probably lies in [this function](https://github.com/jackMort/ChatGPT.nvim/blob/48c59167beeb6ee0caa501c46cecc97b9be8571d/lua/chatgpt/api.lua#L162).

Inspect the command-handling function in lua/chatgpt/api.lua around line 162, starting with how api_key_cmd is parsed and executed. Reproduce the issue with the two configurations in the report; done means commands whose arguments contain spaces return the API key just like the working command.

Written by the indexing model from the issue text.