Allow support for WORKSPACE.bazel files

[UebelAndre]

PR Checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

Issue Number: #1902

What is the new behavior?

Users can now use WORKSPACE.bazel files by setting go_repository_default_config:

load("@io_bazel_rules_docker//repositories:deps.bzl", container_deps = "deps")

container_deps(
    # https://github.com/bazelbuild/rules_docker/issues/1902
    go_repository_default_config = "@//:WORKSPACE.bazel"
)

Does this PR introduce a breaking change?

• Yes
• No

Other information

[alexeagle]

sigh, the messes

[UebelAndre]

For the paper trail. This change could probably be removed depending on the outcome of #1787