Migrate the Chef repo to Cinc Workstation

Cinc Workstation replaces Chef Workstation for driving knife-zero and
Test Kitchen; nodes run (or are moving to) Cinc Client.

- Pin .ruby-version to cinc-workstation
- Move knife config from .chef/ to .cinc/ (Cinc's USER_CONF_DIR) and
  update .gitignore, README, AGENTS and docs accordingly. On-node config
  now lives in /etc/cinc
- Drop the Gemfile/Gemfile.lock; install knife-zero into Cinc
  Workstation's user gem dir with `cinc gem install knife-zero`
- README: rewrite setup/usage for Cinc Workstation
- scripts/postgresql/switch_primary.sh: drop `bundle exec`

doc/ldap.md

@@ -6,7 +6,7 @@ The admin account is `cn=Directory Manager` with the password stored in the
 encrypted data bag `admin_password` item
 
 ```
-$ knife data bag show credentials dirsrv --secret-file .chef/encrypted_data_bag_secret
+$ knife data bag show credentials dirsrv --secret-file .cinc/encrypted_data_bag_secret
 ```
 
 ## Example search (will prompt for password):