test(ssi): added integration and unit tests

• Unit tests for some basic config interactions
• Unit tests for the agent service/controller
• Unit tests for the connection service/controller
• Integration tests for agent module
• Integration tests for the connection module

For the integration tests, a NATS server must be running. If we want to test this in CI we have to make sure it is running in the background.

Signed-off-by: Berend Sliedrecht berend@animo.id