Add GitHub Actions CI workflow for unit tests

[etimofeeva]

No description provided.

[pragmaxim]

@etimofeeva I set the VARs into GH, so please read it like this for the connectivity and integration tests :

  - name: Run unit tests in Docker (no temp file)
    env:
      VARS_JSON: ${{ toJSON(vars) }}
    shell: bash
    run: |
      docker run --rm \
        --env-file <(echo "$VARS_JSON" | jq -r '
          to_entries[]
          | select(.key|test("^BB_RPC_(URL_HTTP|URL_WS)_"))
          | "\(.key)=\(.value)"
        ') \
        -v "$PWD:/src" \
        blockbook-build bash -c "..."

[pragmaxim]

@etimofeeva you need to rebase it on the branch fix-closing-rocksdb-on-shutdown-signal which has connectivity tests done the same way as unit test or integration tests

See https://github.com/trezor/blockbook/blob/fix-closing-rocksdb-on-shutdown-signal/docs/testing.md

there is :

    make test – run unit tests only (note that make deb* and make all* commands always run also test target)
    make test-connectivity – run connectivity checks only
    make test-integration – run integration tests only
    make test-all – run all tests above

and

test-integration: prepare-sources
	cd $(BLOCKBOOK_SRC) && go test -tags 'integration' `go list github.com/trezor/blockbook/tests/...` $(ARGS)

test-connectivity: prepare-sources
	cd $(BLOCKBOOK_SRC) && go test -tags 'integration' `go list github.com/trezor/blockbook/tests/...` -run 'TestIntegration/.*/connectivity' $(ARGS)