Github actions migration

[pl-misuw]

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This change introduces Github actions based build and test.

Two workflows that are similar to current setup: CircleCI -> .github/workflows/buid-test-workflow.yaml BuildKite -> .github/workflows/test-workflow.yaml

Those are being run on [push] event, so every commit for every branch. It might be tweaked to run only for PR's and have PR's blocked until they pass tests, should such need arise.

In current form, it's simple enough, but should cover everything that buildkite and CircleCI did.

As for CircleCI and BuildKite, they can be closed down with follow-up PR, for now we can have both running only to check if we're covering "all bases".