Adding new branch feature/snaa-certificate

Here is the pull request for SNAACertificate implementation, also including a client library and an organization service implementation. It added a new independent feature branch named "feature/snaa-certificate" instead of modifying the code base in the branch develop.

The client library and organization service can be found at: /client-certificate and /organization-service.
In the "snaa" folrder, we have added a package called "eu.smartsantander.cea.certificate".
We have also added an installation document in /organization-service/src/main/resources explaining our SNAA implementation.