Consider making CI bazel cache public for read only access

[rnett]

trafficstars

Bazel allows you to use the build cache in a read-only manner see here. It would be very helpful for local builds if we could make the cache used by the CI available in read only mode for local builds, and potentially automatically set that up (via a bazelrc or maven profile). Currently building from scratch takes several hours for me, which is quite a pain. It would require changing the permissions on the GCP bucket though and I'm not sure if that's something we can do.

cc @karllessard