Generic OpenAI API compliant AI Chat Endopoint configuration

[corradodebari]

Since model server like HF TGI/vLLM/OpenLLM offer their models as OpenAI API REST endpoint, a generic OpenAI end point with a free field for name model could offer an integration point.
In the case of model served by HF TGI, the model name is fixed to "tgi" since the server "serve" only one model at time.
So, this generic option should be added on request into the Model configuration page more than once, to reach out several independent model servers.

[gotsysdba]

make API a LOV of supported API types (like "Generic OpenAI")

[gotsysdba]

Related to #59