Prompt for getting commit messages directly inline

[GordianDziwis]

I would like a command which I could use for a NeogitCommit buffer. This command should insert the commit message. I came this far:

    prompt_library = {
        ["Generate a Commit Message"] = {
            strategy = "inline",
            description = "Generate a commit message",
            opts = {
                index = 10,
                is_default = true,
                is_slash_cmd = true,
                short_name = "commit",
                user_prompt = false,
                auto_submit = true,
                placement = "before"
            },
            prompts = {
                {
                    role = "user",
                    content = function()
                        return string.format(
                            [[You are an expert at following the Conventional Commit specification. Given the git diff listed below, please generate a commit message for me:

```diff
%s
```

With the following config:

```js
-- %s
```
]],
                            vim.fn.system("git diff --no-ext-diff --staged")
                            --,
                            -- vim.fn.join(
                            -- vim.fn.readfile(vim.fn.expand('~/repositories/dotfiles/styleguides/commitlintrc.js')), '\n')
                        )
                    end,
                    opts = {
                        -- visible = false,
                    },
                },
            },
        },
    }

But there is an issue, this prompt only inserts the first line of the commit message. Can anyone help?