Add maven stage yaml for 3.1.0 version

- Step 5 from https://wiki.onap.org/display/DW/CPS+Release+Process
- Change for CPS Core Only

Issue-ID: CPS-1277
Change-Id: I8819f6a73ab84f6e4794181920a903d36e107479
Signed-off-by: mpriyank <priyank.maheshwari@est.tech>
diff --git a/releases/3.1.0.yaml b/releases/3.1.0.yaml
new file mode 100644
index 0000000..1258b26
--- /dev/null
+++ b/releases/3.1.0.yaml
@@ -0,0 +1,4 @@
+distribution_type: maven
+log_dir: cps-maven-stage-master/696/
+project: cps
+version: 3.1.0