Fix mb.py presubmit issues.

* Add a config file for python formatting (.style.yapf).
* Change the default indentation from 4 spaces to 2 spaces.
* Run 'git cl format --python' on a few python files.

Bug: webrtc:13413
Change-Id: Ia71135131276c2c499b00032d57ad16ee5200a5c
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/238982
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Christoffer Jansson <jansson@google.com>
Reviewed-by: Henrik Andreassson <henrika@webrtc.org>
Commit-Queue: Jeremy Leconte <jleconte@google.com>
Cr-Commit-Position: refs/heads/main@{#35500}
diff --git a/OWNERS b/OWNERS
index ac801fe..4702befd9 100644
--- a/OWNERS
+++ b/OWNERS
@@ -17,3 +17,4 @@
 per-file WATCHLISTS=*
 per-file native-api.md=mbonadei@webrtc.org
 per-file ....lua=titovartem@webrtc.org
+per-file .style.yapf=jleconte@webrtc.org