[GH] Download cmake 3.22.1 onto build machines

AndroidX uses this Cmake version which is only available in the canary
channel.

Also re-enabled datastore-mutliprocess on playground and updated
contributing.md doc to include the cmake download instruction.

Fixes: 229400584
Test: Github CI

This is an imported pull request from https://github.com/androidx/androidx/pull/366.

Resolves #366
Github-Pr-Head-Sha: bf4e734a811a8dfed148c13ad751efb050c8644c
GitOrigin-RevId: 71e96b27da8234c84ae32105976df252aa12bdf6
Change-Id: I9a2bf7b109fe98b42957dc45fb28fa9b58e7b2fd
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 54cff69..52813a8 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -40,6 +40,7 @@
 
   ```bash
   sdkmanager --install "ndk;23.1.7779620"
+  sdkmanager --install "cmake;3.22.1" --channel=3 #channel 3 is the canary channel
   ```
 
   Next, you need to set up the following environment variables: