function to toggle panel

Hello,

First off, thank you for this awesome plugin! Just starting to use it in certain situations and it amazes me how it works.

I recently created a toggle function to disable/enable copilot:
```
" custom global var for toggle function
let g:copilot_enabled = v:true

function! ToggleCopilot()
if g:copilot_enabled
Copilot disable
let g:copilot_enabled = v:false
else
Copilot enable
let g:copilot_enabled = v:true
endif
Copilot status
endfunction

nnoremap c :call ToggleCopilot()
```

And wanted to create something similar with `:Copilot panel`.

Any input in how I could achieve this is appreciated?

Thank you,
Dave

首先閱讀 `:Copilot panel` 命令的實作，以及現有的 `:Copilot enable` 和 `:Copilot disable` 命令。確定切換功能應如何與面板狀態互動，然後驗證呼叫新函式是否會一致地交替改變面板行為。

由索引模型根據 Issue 內容生成。