Docs: Add documentation on how to run tests

[kanow]

Goal

I as a user/developer has all informations how to execute tests

Acceptance Criteria

• [ ] explain how to execute test with docker (not in the local system)
• [ ] explain how to execute functional tests with a database

Additional information

I start to execute some tests and had errors. I'm searching for information to execute tests in the documentation but the infor not detailed enough.