[docker-sonic-mgmt]: Add docker-ce-cli to sonic-mgmt container (#3868)

In the scope of migration from docker shell plugin to docker connection plugin, we need to have docker-ce-cli installed in docker-sonic-mgmt. Azure/sonic-mgmt#1269

Added docker-ce-cli package to docker-sonic-mgmt.

dockers/docker-sonic-mgmt/Dockerfile.j2

@@ -71,6 +71,19 @@ RUN pip install ipaddr \
     && pip install nnpy    \
     && pip install dpkt
 
+# Install docker-ce-cli
+RUN apt-get update                  \
+    && apt-get install -y           \
+      apt-transport-https           \
+      ca-certificates               \
+      curl                          \
+      gnupg-agent                   \
+      software-properties-common                                                                                   \
+    && curl -fsSL https://download.docker.com/linux/ubuntu/gpg | apt-key add -                                     \
+    && add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"    \
+    && apt-get update                                                                                              \
+    && apt-get install -y docker-ce-cli
+
 # Install Microsoft Azure Kusto Library for Python
 RUN pip install azure-kusto-data==0.0.13 \
                 azure-kusto-ingest==0.0.13