Add a way to refer to some file with a prompt-based template

[vldF]

Based on #7100

Sometimes, we would use prompts as some kind of 'functions'. In yaml/md file of some prompt, we 'declare' its body (with description of an action it does). Also, we do need to use 'arguments'. As far as I understand, there is no such concept right now. This discussion approaches a way to imitate limited argument-like external data 'pass' to such 'functions'.

We can introduce something like macro for selected file for prompts. Also, we can add special context menu item for files and directories. This menu shows all available prompts contain such macro and introduces a way to apply one of them in one click. When user click on such menu item, it puts a new message to the Continue message input block. Macro in the prompt replaces to the path to the file. File is also being added as a context item.

Use cases

1. Unit tests generation for the whole file in one click
2. Single file code review
3. Easy code prettifications

[vldF]

It seems feature like this is already present in VS Code https://docs.continue.dev/customize/deep-dives/vscode-actions