feat: pipe buffer output to new document

[majiayu000]

Summary

• add pipe buffer actions for terminal output and for opening output as a new document
• avoid a default key binding; document how to bind pipe_buffer/pipe_buffer_doc
• add a DocPipe type to label pipe output documents

Motivation

Follow-up to feedback on #944 about offering pipe output as a new document and avoiding a default | binding.

Testing

• go test ./oviewer

[noborus]

Since I did not receive a reply to my comment on #944, I will comment here.
I cannot merge changes that add new features without a clear use case or intended usage.
Could you please explain in more detail how you expect each of pipe_buffer and pipe_buffer_doc to be used?
Are both actions necessary as separate features, and in what scenarios would each be used?
Understanding the intended use cases will help determine whether both are needed or if one is sufficient.