feature/slapd testing

[cutoffthetop]

Added

• set up integration tests against slapd using docker compose

TODO

• create fixtures for slapd-only and patched_connector-only testing based on old mocked_ldap fixture
• keep mocked_ldap fixture for running tests against both
• decide for each test which flavor(s) to run (some tests don't make sense for patched_connector)
• continue with setting up slapd tests for backend