.gitlab-ci: add job to deploy doxygen docs on remote server

Add ci job in deploy stage to build Doxygen docs and upload html artifacts into docs.svc.ostc-eu.dev

The job runs only in protected branches because the ssh key variables are protected

Artifacts are uploaded to a remote ssh server using ssh key stored in $SSH_PRIVATE_KEY variable and the passphrase if exists is stored in $SSH_PASSPHRASE

Signed-off-by: Francesco Pham francesco.pham@huawei.com