Add githubAction to build & push docker image on github release published event. (#881)

fixes #880 👍 

Update Dockerfile
- fix alpine image version
- add RELEASE_VERSION build arg

Add githubAction to build & push docker image on github release published event
- add github workflow file
- add dependabot file to automatically propose PRs on githubActions version update*

> ⚠️ *Note1: you will have to add `DOCKERHUB_USERNAME` and `DOCKERHUB_TOKEN` as github secrets in order for the 
> ⚠️ *Note2: github dependabot support must be enabled in order for this action to work
githubAction to be able to login to the dockerHub and push images on it 👍
> *Note3:  we can add other dependabot entries in order to update Go modules and Dockerfile base images 👍 (i.e `FROM` parts)

.github/dependabot.yaml

@@ -0,0 +1,10 @@
+version: 2
+updates:
+  # Maintain dependencies for GitHub Actions
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    pull-request-branch-name:
+      # Separate sections of the branch name with a hyphen
+      separator: "-"