Add integration tests

[tkilias]

Background

• Currently, we only use unit tests with mocks for exaslct apis
• If these apis our mocks will be wrong without knowing us

Acceptance Criteria

• Add integration tests for at least exaslct apis, for github release it might be not so easy

[tkilias]

This ticket was mostly done with https://github.com/exasol/script-languages-container-ci/pull/27. The only thing where we don't have an integration test for is the github release. However, this is, in general, difficult to test