This is not UiPath Robot specific, but Linux specific. If you have the rootCA.crt file you can use the following dockerfile to create a docker of your own that includes the self-signed certificate.
ADD rootCA.crt /usr/local/share/ca-certificates/uipath.crt
RUN chmod 644 /usr/local/share/ca-certificates/uipath.crt && /usr/sbin/update-ca-certificates
The rootCA.crt certificate should be in the same folder as the Dockerfile and you should run the build command
docker build -t myrobot-self-signed-cert . then run the new docker image that you have build using:
docker run -e LICENSE_AGREEMENT=accept -e ORCHESTRATOR_URL="https://cloud.uipath.com/organization/tentant/orchestrator_" -e MACHINE_KEY="$KEY" -tid myrobot-self-signed-cert