* Proof-of-concept writing tar to stdout
A quick and dirty experiment showing one possible approach for
writing certificates to stdout. Demonstrates a possible solution
to #29262.
DO NOT MERGE AS IS. IN NO WAY PRODUCTION READY.
* Fix timestamps
* Adds `--tar` option to `auth sign`
Adds an option to bundle the certificates generated by `tctl auth sign`
into a tarball and writes that tarball to stdout.
This is to facilitate extracting credentials from environments with
limited access to the filesystem and tools like a shell, tar and so
on, e.g. distroless Docker images.
Example usage:
```
$ kubectl exec ... -- tctl auth sign --user alice --format openssh -o alice --tar | tar xv
x alice-cert.pub
x alice
```
* Reroutes helper mesg to stderr when straming tar file to stdout
Trent Clarke
02d2f8bcf8