Feature request: Make prompt templates customizable

[doggy8088]

I'd like to suggestion providing a way to customize the prompt template when user needed.

Here is the proposal:

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Provide two ways to customize the prompt templates:

1. Check if the folder exists: $HOME/.config/codegpt/prompt_templates

   If the folder exists, read the templates from the folder automatically.

2. Set codegpt.prompt_template_path config

   codegpt config set codegpt.prompt_templates_path "$HOME/.config/codegpt/prompt_templates"