[rbe] Local registry: build config diff ids from layers

[gabrielrussoc]

The local registry gets the image config as input, which contains the hashes of all the layers inside of the image.
We were simply returning it but it turns out the hashes of the layers in the config does not always match the actual layers.
This is caused by a weird interaction in Databricks internal rules where we have a docker layer as a parent of a docker base like docker_layer -> docker_base -> docker_layer.

Essentially, if the docker layer changes, we are required to rebuild the docker_base but there is nothing enforcing that today (see https://github.com/databricks-eng/universe/blob/bf55a02cb20c5bb72992a4bb401212bea69f9397/bazel/rules/docker.bzl#L2051).

When that happens, we get errors like the ones seen on:
https://runbot-ci.cloud.databricks.com/build/Unit-Compile-Pr/run-logs/45377642

layers from manifest don't match image configuration

So to workaround this we make the behaviour of the loader_tool to be the same as the original incremental loader: we overwrite the hashes in the config using the values computed from the actual layers:

rules_docker/container/incremental_load.sh.tpl

Line 75 in da6dc62

"diff_ids": [$(join_by , ${diff_ids[@]})],