Introduce linters to protect and maintain code quality.

[tyzerrr]

SSIA
I prefer to introduce this, built by Netflix.

[tyzerrr]

@draeger Could I take this issue?
I will make CI/CD pipeline with Github Actions.

Goal is below.
[Goal of this issue]

1. Build the way to check whether all tests and all lint check pass or not.
2. Migrate from maven to gradle, this is related Migrate from Maven to Gradle #77.

If I can understand how to migrate from Gradle, I'll also take this issue.
If you think this is fine, could you assign me, and also could you make me Maintainer of this project?
I think this is one of the greatest contribution.