Understanding the CI

Our CI pipelines are split according to their responsibities:

1. Unit Testing pipeline
2. Linter pipeline

Both pipelines are required to pass before merging a pull request. We do not target the Squeak trunk as that proved too unreliable a target. We also only test on linux, as the macos pipeline does not work with our unit tests. This is due to the way we download tdlib and can be fixed in the future. We also wanted to create a pipeline executing tests against the Telegram Test Data Center, this also was not implemented due to time constraints but it probably is the best integration test one could run.