Enhancement: Volume mode for files not directories

If you want to mount a single config file into a container, you might use

-v $(pwd)/nginx.conf:/etc/nginx/conf.d/site.conf:ro

If nginx.conf does not exist, it will be created as a directory on the host, and probably raise an error:

Are you trying to mount a directory onto a file (or vice-versa)? Check if the specified host path exists and is the expected type

It would be useful if there were a way to indicate that the volume refers to a single file. For example:

-v $(pwd)/nginx.conf:/etc/nginx/conf.d/site.conf:fro
                                                 ^-- for file

In this example, :f or :frw would indicate a read-write file, and :fro would indicate read-only. If :fro is used and the file doesn't exist, it would raise an error.

There should also be corresponding syntax for VOLUME and a long syntax flag for Docker Compose files.

No source files, tests, or entry points are named in the issue. Trace volume-option parsing in the CLI first; completion would cover the proposed file-mode syntax, its missing-file behavior, and corresponding VOLUME and Compose forms, with tests for each.