Remote execution images

The Dockerfiles for remote execution images are autogenerated to pin all versions and allow for updates at the same time. To repin the image hashes and package versions:

# With Bazel
bazel run //bazel/remote_execution_container:repin_dockerfiles --config=local

# Without Bazel
./repin_dockerfiles.sh

To change the image contents, edit repin_dockerfiles.sh.