Create shell script to synthesize a test cert chain

[thomas-fossati]

Repurpose the RATSd script to create a 3-level chain including:

1. root CA certificate with subject name "Acme Inc."
2. intermediate CA cert with subject name "Acme Gizmos"
3. an end-entity cert with subject name "Acme Gizmo CoRIM signer"

The name are expressed purely as CNs (i.e., no SAN).

The certs are in DER format, rather than PEM.

The synthesized chain will be stored in a new misc folder under the veraison/corim repo.
The script will be stored in the scripts folder under the veraison/corim repo.

Also, add a new target to the top-level Makefile to regenerate the chain.

[Akhilesh-max]

Completed by #165