Support --excludeExternalTargets #22
Description
The external package no longer exists when --noenable_workspace is specified, causing bazel-differ to error:
ERROR: Skipping '//external:all-targets': no such package 'external': //external package is not available since the WORKSPACE file is disabled, please migrate to Bzlmod or temporarily enable WORKSPACE via --enable_workspace. See https://bazel.build/external/migration#bind-targets.
bazel-diff added the --excludeExternalTargets option to compensate. Tinder/bazel-diff#236 / Tinder/bazel-diff#246