notebooks: generic input for file block

Created by: novoselrok

I'm splitting up the large file block PR into smaller chunks for easier reviewing. See the entire thing here: https://github.com/sourcegraph/sourcegraph/pull/28274

This PR adds a generic input to be used in the file block. It will be used for the four inputs we need: repository name, file path, revision, and line range. It also supports optional suggestions (we'll use them for repositories and file paths).