Ability to set up logjam in advance for a given project

## Context

It seems desirable to leave logjam collecting logs as soon as possible, and automatically. That way, when an issue worth investigating pops up, one already had nice logs for it, ready for inspection.

This logjam activation should go on a per-project basis, given that different projects can use different logging frameworks.

## Task

Either:

* Figure out + document how to invoke cider.log.repl from user.clj (which has some complexities)
* Document how to provide a hook on the Elisp side.

## See also

https://github.com/clojure-emacs/cider-nrepl/pull/773#discussion_r1230969406