Add system tests

## Description

There should be a way to automatically test the Python SDK in a real container with a working Ankaios cluster. Having this, we should be able to minimize the problems that might appear during development and corner cases that are not tested correctly in the moment. The software tests should also be mandatory to run on every PR, to be sure that the functionality of the SDK is no affected.

## Goals

Software tests are implemented and are testing at least once all of the methods of the Ankaios class that communicate with the Ankaios cluster.

## Final result

### Summary

**To be filled when the final solution is sketched.**

### Tasks

- [ ] Investigate a way to implement software tests.
- [ ] Investigate what cases should be tested with software tests.
- [ ] Implement software tests.
- [ ] Add the software tests to GitHub actions.

ファイルやテストのエントリーポイントは指定されていません。まず、稼働中の Ankaios クラスターと通信する Python SDK の Ankaios クラスのメソッドを洗い出し、次に実際のコンテナと GitHub Actions でそれらを実行する方法を調査してください。すべての該当メソッドが少なくとも一度テストされ、システムテストがすべての pull request で実行されれば完了です。

索引モデルが issue の本文から書いたものです。