Add GitHub action

[nam-jaehyun]

Add GitHub action to test the code and push a new image to DockerHub.

[nyrahul]

#5 added following with GH actions:

• build/push the image to DockerHub on push to main branch.
• regular checks (lint, gosec, fmt)

[exitflynn]

Are the tests which are yet to be implemented in the GH actions already written (like in case it's only a matter of porting them from a different repo) or do we need to be write them from scratch here? 🤔

[nyrahul]

Currently, in kubearmor-relay, there are no tests. So the tests have to be written from scratch.