Add default certificates for a1-interface

The default certificates are in folder /usr/src/app/cert
The default certificates can be overriden by mounting a volume in 'docker run' command or in a docker-compose.yml file
ex:
in 'docker run':
docker run -it -p 8085:8085 -p 8185:8185 -e A1_VERSION=OSC_2.1.0 -e REMOTE_HOSTS_LOGGING=1 --volume "$PWD/certificate:/usr/src/app/cert" a1test
in 'docker-compose.yml':
volumes:
      - ./certificate:/usr/src/app/cert:ro

Issue-ID: NONRTRIC-218
Signed-off-by: ecaiyanlinux <martin.c.yan@est.tech>
Change-Id: I0db70fe403f8190257bb7fe910d08ab59b3b8ed3