Create GitHub workflows for CI/CD

### Context?
GitHub workflows can be used to automate some tasks which would generally take time doing manually and are better automated.

### What to do?
Create workflows for some common scenarios like:
- Checking whether code builds successfully in pull requests and when PRs are merged in master branch. See - #8
- Updating and pushing docker image whenever the master branch is updated. See - #9
- Running tools like gofmt and golint in PRs to keep clean code. See - #10

### Resources:
- A guide on Github actions and workflows - https://docs.github.com/en/actions
- Gh workflows syntax guide - https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions
- Go formatting tools - [golint action](https://github.com/golangci/golangci-lint-action), [gofmt](https://pkg.go.dev/cmd/gofmt)

### NOTE
Try picking any one of the scenario and comment on the respective issues to show your interest. We'll assign it to you.