PR #17034 Added the capability to specify per volume mount propagation mode. This added the shared/slave/private options to the --volume option.

As was mentioned in #17034 (comment), the documentation for this was supposed to be updated in a follow-up PR, but that doesn't seem to have happened.

Places where it is missing or completely underwhelming:

• https://docs.docker.com/engine/reference/run/
• https://docs.docker.com/engine/reference/commandline/run/
• https://docs.docker.com/engine/userguide/containers/dockervolumes/

Just Ctrl+F for the word "slave" on those pages, and see that it is missing, or has no explanation.

This was originally brought up in #20555.

cc @thaJeztah