### Summary
`rootfs` create writes proc/self/exe as a symlink, but currently passes
the previous regular file buffer to `ArchiveWriter.writeEntry`. This
change switches that symlink entry to nil, which matches archive writer
expectations.
### Test
Archive tests pass.
- Motivation is to be able to add the `swift-backtrace-static` binary as
needed.
- Use singlular `--add-file` and `--label` options since both accept
multiple invocations with single values each.
Example usage:
```bash
./bin/cctl rootfs create \
--vminitd vminitd/bin/vminitd \
--vmexec vminitd/bin/vmexec \
--add-file /Users/john/.swiftpm/swift-sdks/swift-6.2-RELEASE_static-linux-0.0.1.artifactbundle/swift-6.2-RELEASE_static-linux-0.0.1/swift-linux-musl/musl-1.2.5.sdk/aarch64/usr/libexec/swift/linux-static/swift-backtrace-static:sbin/swift-backtrace \
--label org.opencontainers.image.source=https://github.com/apple/containerization \
--image vminit:latest \
bin/init.rootfs.tar.gz
```
This refactors the rootfs command to produce an image and have the
ability to create an ext4 formatted block of the init filesystem
directly from the command.
closes#220
Signed-off-by: crosbymichael <michael_crosby@apple.com>
Manoj Mahapatra