[example] Code Signing Certificate Request w/ Attestation Chain

Code Signing Certificate Request w/ Attestation Chain:
```
ykman piv keys generate 9c pubkey.pem -a ECCP384
ykman piv certificates request 9c pubkey.pem codesign.csr --subject "CN=Example,DC=example.com"
ykman piv keys attest 9c attest.pem
ykman piv certificates export f9 - > attest.pem
```