Create workflow to build the Docker image on any branch

The Docker image will be build on any branch, to ensure the healthiness
of this process. Apart from that, the "build_and_release" job will only
be executed when we create a new tag in the repo.

.circleci/config.yml

@@ -29,10 +29,16 @@ jobs:
 
 workflows:
   version: 2
-  build-master:
+  build-branch:
+    jobs:
+      - build
+
+  build-on-tag:
     jobs:
       - build_and_release:
           context: conntest-dockerhub-release
           filters:
             tags:
               only: /.*/
+            branches:
+              ignore: /.*/