Unlike with gnu make, mixed version testing with bazel uses a package-generic-unix for the secondary umbrella rather than the source. This brings the benefit of being able to mixed version test releases built with older erlang versions (even though all nodes will run under the single version given to bazel)
This introduces new test labels, adding a `-mixed` suffix for every existing test. They can be skipped if necessary with `--test_tag_filters` (see the github actions workflow for an example)
As part of the change, it is now possible to run an old release of rabbit with rabbitmq_run rule, such as:
`bazel run @rabbitmq-server-generic-unix-3.8.17//:rabbitmq-run run-broker`
Adds WORKSPACE.bazel, BUILD.bazel & *.bzl files for partial build & test with Bazel. Introduces a build-time dependency on https://github.com/rabbitmq/bazel-erlang
Philip Kuryloski