Turn Bazel CI into a reusable setup for other people

It would be nice to polish our Bazel CI and turn it into a reusable CI setup following our best practices that other people could use to run a similar service for their open-source project or company.

Start by reviewing the existing Bazel CI setup in this repository and identifying how it currently runs. Define the reusable setup's scope and best practices for other open-source projects or companies, then verify that the resulting configuration can support a similar service outside this repository.

Written by the indexing model from the issue text.