Add client Q branch (#65)

* We want to try engagement specific Q branch pairing. It'll be just
    like regular Q branch, but only for agents deployed at a given
    client. We're trying this as an experiment to see if we can improve
    knowledge sharing, uncover common patterns, and sharpen our pairing
    skills.

config/matchmaking.yml

@@ -1,4 +1,9 @@
 default: &default
+  client_q_branch:
+    active: true
+    channel: rotating-client-q-branch
+    schedule: monthly
+    size: 2
   coffee_time:
     active: true
     channel: rotating-coffee-time