add google gemini

[wangzhankun]

Notice: I have only tests the google gemini, because I have no openai api.

• create interface AiAssistantInterface as all ai models father class
• class GoogleGeminiApi and class OpenAIAssistant implements AiAssistantInterface
• add provider settings and change the default settings into:

const DEFAULT_SETTINGS: Settings = {
	provider: "openai",
	assistantSettings: new Map<string, AiAssistantSettings>([
		["openai", {
			apiKey: "",
			modelName: "gpt-3.5-turbo",
			imageModelName: "dall-e-3",
			maxTokens: 500,
			replaceSelection: true,
			imgFolder: "AiAssistant/Assets",
			language: "",
		}],
		[
			"google", {
				apiKey: "AIzaSyAthMXmBkx4E7S7E9pdzo7xUiVShxvCj5A",
				modelName: "gemini-pro",
				imageModelName: "gemini-pro-vision",
				maxTokens: 1000,
				replaceSelection: true,
				imgFolder: "AiAssistant/Assets",
				language: "",
			}
		]
	])
};

• to select model from setting tab for different provider, implement GoogleGeminiSettingTab in src/google_gemini_api.ts and OpenaiSettingTab in src/openai_api.ts