Add Github actions for linting and testing

[butovsky]

Related to #23 and #43.

This PR adds a simple .yml workflow for linting and testing the code prior to merging with main. The workflow is a Development one, but idk whether we would need Staging/Production CI logic on this project haha.

For now, it works only on main commits + on PRs headed towards main. There is no problem in extending these triggers in the future btw.

You can see the example of such Action right in this PR in my fork. Don't pay attention to the failing checks, for now this is caused by #46. But, I guess, after completing this PR and resolving linting issues, it will be great to prohibit merges on failed CI/CD in project settings.