promp file path can be passed by parameter

### Describe the feature or problem you'd like to solve

_No response_

### Proposed solution

Currently, you are allow to do ```copilot -p "prompt"```
If prompts are large, or contain quotes or other special characters, it would be better to have the prompt in a file and pass it to the cli (ex ```copilot -f /prompt.md```) instead of having to use cat or other commands.

### Example prompts or workflows

_No response_

### Additional context

_No response_

Start by locating the CLI argument handling for the existing `copilot -p "prompt"` flow. Add support for the proposed `copilot -f /prompt.md` form, using the file contents as the prompt, and verify that large prompts and special characters are passed correctly.

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