feat: Make trouble.nvim optional

[Uzaaft]

An attempt at making trouble optiona.
@jackMort What do you think about this approach? If it's alright I can fix the docs as well.

Disclaimer: Couldn't test this since I don't have an openai user anymore

[petobens]

Please revert; this gives the following error:

Failed to run `config` for ChatGPT.nvim

...ocal/share/nvim/lazy/ChatGPT.nvim/lua/chatgpt/config.lua:9: module 'trouble' not found:
^Ino field package.preload['trouble']
^Icache_loader: module 'trouble' not found
^Icache_loader_lib: module 'trouble' not found
^Ino file './trouble.lua'
^Ino file '/usr/share/luajit-2.1/trouble.lua'
^Ino file '/usr/local/share/lua/5.1/trouble.lua'
^Ino file '/usr/local/share/lua/5.1/trouble/init.lua'
^Ino file '/usr/share/lua/5.1/trouble.lua'
^Ino file '/usr/share/lua/5.1/trouble/init.lua'
^Ino file '/home/pedro/.local/share/nvim/lazy-rocks/telescope.nvim/share/lua/5.1/trouble.lua'
^Ino file '/home/pedro/.local/share/nvim/lazy-rocks/telescope.nvim/share/lua/5.1/trouble/init.lua'
^Ino file './trouble.so'
^Ino file '/usr/local/lib/lua/5.1/trouble.so'
^Ino file '/usr/lib/lua/5.1/trouble.so'
^Ino file '/usr/local/lib/lua/5.1/loadall.so'
^Ino file '/home/pedro/.local/share/nvim/lazy-rocks/telescope.nvim/lib/lua/5.1/trouble.so'
^Ino file '/home/pedro/.local/share/nvim/lazy-rocks/telescope.nvim/lib64/lua/5.1/trouble.so'

# stacktrace:
  - /ChatGPT.nvim/lua/chatgpt/config.lua:9 _in_ **default_quickfix_cmd**
  - /ChatGPT.nvim/lua/chatgpt/config.lua:191 _in_ **defaults**
  - /ChatGPT.nvim/lua/chatgpt/config.lua:211 _in_ **setup**
  - /ChatGPT.nvim/lua/chatgpt.lua:24 _in_ **setup**
  - ~/.config/nvim/lua/plugin-config/chatgpt_config.lua:6
  - ~/.config/nvim/lua/plugins.lua:157 _in_ **config**