[automerger skipped] [DO NOT MERGE] Add RBE mk file to support bootstrapping...

[automerger skipped] [DO NOT MERGE] Add RBE mk file to support bootstrapping RBE and setting relevant am: 7298be1b am: edd7e730 -s ours

am skip reason: subject contains skip directive

Original change: https://googleplex-android-review.googlesource.com/c/platform/build/+/12468471

Change-Id: Ied1f9813b9c799fa601af4d5bc3e9a19dc9baf1d