Added keybindings for the Sesman REPL session management commands to the Clojure
layer, following the Spacemacs keybinding conventions.
https://docs.cider.mx/cider/0.23/usage/managing_connections.html
Sesman has been a part of CIDER for many versions now and provides session
management for nREPL connections (in fact any connections).
Sesman keybinds are placed in the `SPC m c` menu, providing a cleaner separation
between sending code to the repl and session management.
See issue #12593 and PR #13140 which covers the background for the design of
these additional keybindings.
Formatting the region and defun keybinds have been added, along with formatting
for edn files. Moved to `=` menu to match Spacemacs convention.
Evaluation up to point keybinding has also been added.
Documentation in the README has been updated to complete the description of the
existing Clojure layer, as well as including details specific to the new
keybindings.