Rewrite connector base class

[nor3th]

Features to implement

connector class

• [x] connector base class, subclass for each connector type (see UML diagramm)
• [x] use mixins for external connections (HTTP proxy support)
• [x] move any logic besides data fetching and stix submitting from the connector itself to the base class
• [x] dedicated logger
• [x] a cleaner connector structure
• [ ] add telemetry metrics (open telemetry or prometheus)

other

• [x] introduce testing capability for connectors
• [x] move the connector settings (away from the docker config) to the OpenCTI platform (a new connector should push a config template to opencti which the admin can then configure)

Optional implementations

• [x] Design the connector <-> OpenCTI link in a modular way, to maybe implement AWS or Azure Messaging Brokers
• [x] ~Design Celery PoC~ (Done, Celery is out since it can't handle Stream processing)