Add docker stage yaml for 3.1.0 version

- Step 6 from https://wiki.onap.org/display/DW/CPS+Release+Process
- Change for CPS Core Only
- Took containers.version from log https://jenkins.onap.org/job/cps-maven-docker-stage-master/690/consoleFull
- Took ref from the latest commited change in CPS Repo https://gerrit.onap.org/r/c/cps/+/130923

Issue-ID: CPS-1278
Change-Id: I9d77c306da9649bf898a9ac405fcae56b1762da9
Signed-off-by: mpriyank <priyank.maheshwari@est.tech>
1 file changed