CertificateClient and KeyStoresFactory support multiple Sub-CA certificates in the trust chain

Here is the previous certificate Hierarchy,

    Root CA Certificate

   /                                  \

Sub-CA Certificate     Sub-CA Certificate

/                           \

DN1 Cert             DN2 Cert

Following is the new certificate hierarchy,

    Root CA Certificate

   /                                  \

Sub-CA Certificate     Sub-CA Certificate

/                           \

DN1 Cert             Sub-CA Certificate

                               /                 \

                       DN2 Cert         DN3 Cert

We need to refactor CertificateClient implementation to support multiple Sub-CA Certificate in the trust chain.