Run Perch in analyzer

[kahst]

We should allow people to run Perch (or similar models) as custom model in the analyzer. Yet, we need to read the target sampling rate and segment length (Perch uses 5 seconds instead of 3) and set these accordingly. So, we could look for a model config json and set our config values based on that, if we don't find a config json, we use our default values. Running non-BirdNET models should then be documented. We could think about also supporting OpenSoundscape models and Koogu models the same way.