feat: model_present in status

[toschoo]

Problem

Client applications want or even need to know if the current default model (from the config) is present or not, i.e. if a download will be necessary when the model is used. Currently, client applications abuse the progress field from the status. But that is not reliable.

Solution

Provide a flag in the status "model_present". This flag is set when edgen starts, when the config changes and after download. To test if the model is present, the hf-hub client should be used.