Gemini Completion feature

[BlazingRockStorm]

Add Completion feature for Google Gemini

[BlazingRockStorm]

@alchaplinsky can you help me? I don't know where is wrong

In the new #complete method that I'm developing
generate_completion_options(prompt, options) returns {:contents=>[{:role=>"user", :parts=>[{:text=>"Hello"}]}], :generationConfig=>{}}. the same as in the #chat method

but the response is nil