push to Docker Hub action

[ks6088ts]

What this PR does / why we need it

• add a GitHub Action for pushing built docker image to Docker Hub

Which issue(s) this PR fixes:

Fixes #6

Does this introduce a breaking change?

[ ] Yes
[x] No

Pull Request Type

What kind of change does this Pull Request introduce?

[ ] Bugfix
[x] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Documentation content changes
[ ] Other... Please describe:

Additional Information

ref. ks6088ts/template-go#6