The purpose of this is to be able to install a composition policy that
describes which types are incompatible and that will be enforced during
call creds composition.

If this functionality is wanted it will be done in an additive function in
the API like :

void grpc_call_credentials_set_composite_policy(
  grpc_call_credentials_composite_policy policy);

The encoding of the issuer field in this cert is now a PRINTABLESTRING
as opposed to UTF8STRING in the previous server1.pem which was causing
the Go issue.

Fixes #4086.