recipes.cfg: Set bot_commit option.

This will tell the autoroller to set Bot-Commit+1 instead
of TBR and self CR+1.

Change-Id: I9463924e3a8f4ccc2f96cb68f8d1c517031c8369
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2684329
Reviewed-by: Jason Clinton <jclinton@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Auto-Submit: Edward Lesmes <ehmaldonado@chromium.org>

infra/config/recipes.cfg

@@ -9,7 +9,8 @@
       "automatic_commit": true,
       "tbr_emails": [
         "iannucci@chromium.org"
-      ]
+      ],
+      "bot_commit": true
     }
   },
   "canonical_repo_url": "https://chromium.googlesource.com/chromium/tools/depot_tools.git",