Move licenses_file to separate output group

When packaging outputs via rules_pkg we should not include the
licenses_file by default. To avoid that, move it to its own output
group.

With this change:
bazel cquery --output=files //examples/sboms:write_sbom 2> /dev/null && \
bazel cquery --output=files //examples/src:check_server 2> /dev/null
bazel-out/darwin-fastbuild/bin/examples/sboms/write_sbom.txt
bazel-out/darwin-fastbuild/bin/examples/src/server_report.txt
bazel-out/darwin-fastbuild/bin/examples/src/server_licenses.txt

Before this change those commands would include:
bazel-out/darwin-fastbuild/bin/examples/sboms/_write_sbom_sbom_licenses_info.json
bazel-out/darwin-fastbuild/bin/examples/src/_check_server_licenses_info.json